All are pictured below, in order. I'd be curious to hear anyone else's additional thoughts or different ideas, but these are my picks based on watches I've owned and/or experienced first hand, as well as my own personal taste, with reasoning behind each pick. I was going to add some honorable mentions, but the reality is that there are hundreds that could fit into that realm and I'm not interesting in listing them all out.
Vintage inspired quartz chronograph: $140 Lorus RT351GX9
There are a few in this category, like most offerings from Dan Henry, but for me nothing beats the classic boxy case design and panda dial layout of the Lorus RT351GX9, at almost half the price tag of the others too! Great look and feel, though a terrible folded link bracelet. If you are a "must have bracelet" kind of guy, this isn't a watch for you, unless you've got no arm hair and no taste for modern quality metal. If you like tin foil looking and sounding bracelets, then look no further! But for those of us with taste, this thing looks and feels never better than when it's on a nice cognac leather strap with cream stitching and a subtle 3mm taper to the clasp!
Automatic chronograph: $400 Roter Stern "Red Star" chronograph
A solid quality Chinese copy of the 7750 is at the heart here, with very nice perlage finish and high beat rate. It comes in a few different color ways, my preference is for the beautiful cream dial variant as pictured below, but there's a nice army green and jet black options as well. There's great color contrasting on each dial with panda-like design, except for the black dial which is all blacked out with red accents. My only dislike was the no click bezel. I've never been a fan of free moving bezels, however I will say that it doesn't move easily, as there's a definitive amount of force and intent required to budge it one way or the other. Also, this isn't a diver, so a free moving bezel isn't detrimental to the design and propose of it (unlike Vostok amphibia which are absurd and antithetical to the concept of a "dive watch", with easily free moving bidirectional bezels and acrylic crystals. Which is why you won't see one listed here). Hard to beat an auto chrono for under $500!!!
Vintage inspired automatic diver: $350 Bulova Oceanographer
For the case dimensions it wears very reasonable, as the lugs are basically built into the large cushion case, making it appear and wear very reasonable. It's got the classic Doxa diver look with great bezel action and very unique indicies markers. It's a reissue of the old popularized "devil diver", giving it a rich history too! Several color options too choose from make this a must have in any collection as far as I'm concerned. In fact, it's the only on this list that is currently in my collection with no plans of getting rid of ever.
Quartz diver: Casio duro
I don't think this one needs much for introduction. The reason I chose this over the dozens of other options from the likes of Seiko, Citizen, etc is because of the price tag, and I hate seiko! At under $50, coming in both a beautiful sunburst blue and black dial option, I don't think one could do any better. That said, this category really is flooded and there is almost no wrong one can do here. So the ocean is yours to sift through, pun intended. I just think that this one especially deserves, and usually gets, the proper nod from almost every collector, and for very good reason!
Quartz pilot: Bulova Lunar Pilot $350
I don't think much needs to be said here as this watch speaks for itself! Another reissue from Bulova here, with rich history and a beautiful, timeless design. And that movement, I mean come on, have you watched the sweep of the seconds hand? Oof! Speedmaster eat your heart out, and at a fraction of the cost! High accuracy quartz with an extremely high beat chrono seconds hand is very ill-advised to overlook! Some will complain about size here, but come on, it's not that much bigger than the Moon watch it's designed to look like so really, I find that argument flat.
Manual mechanical pilot: $150 Parnis pilot
Look, there are dozens of choices to make in this category, with hundreds of options, but when it comes to affordability my first go to is Parnis. The quality is just there, it really is, and with a simple manual wind movement there's not much that can be screwed up. This is a category I really don't much care for myself, but I feel one would be remiss in not experiencing one of these classics, as it really is a pillar of the watch collecting journey. There are several case sizes to choose from, dial layouts and colors as well, most fall within 44-48mm, and they're relatively thin, compared to most on this list, which helps cut down on the perceived size of it.
Automatic dress: $120 Orient Bambino
I mean, really, who doesn't already know about the Bambino? Beautiful, classic, elegant and simple dress watch design with several different versions, variants and color options to choose from. I'm not at all a dress watch fan, but even these make me think twice about adding one back to my collection. They can be had for anywhere from $85-150 depending on which version, case color, dial option, etc you choose.
Manual wind chronograph: $190 Alpha Daytona
The always touted ST19 beats at the center of this piece. Derived from the old Swiss Venus manual chronos from yesteryear, these movements are just one of the most beautiful things to see. The Alpha Daytona is of course an homage, and I know I could've chosen other options in this category that aren't homages, like the Seagull 1963 reissue, but I don't like those other options and they're almost double the cost with half the QC as far as I'm concerned, and I know, I've had both! I've never had bad luck with an Alpha, ever. The quality control is just phenomenal here. This particular piece is a really nice rendition with clean finishing and smooth movement and crown actions to boot! There are about a dozen color way options to choose from, in both dial variants and case finishes. Hard to beat bang for buck quality here folks!
Automatic GMT: $150 Alpha GMT-Master
Yes I know, broken record here and another homage, but what can I say, when it's done right, it's hard to beat! Well, Alpha does things right! My preference here is the "Blueberry" option. They come in a cream or white dial with a beautiful blue (almost bordering on purple) GMT bezel insert. Another solid quality Chinese GMT movement copy, this beating at 21600, but on the smaller dial it's almost impossible to notice the difference. This has the second best jubilee bracelet I've ever worn, runner-up only to my buddies DJ11 I tried for a week!
Digital: $25 Casio "Casino Royale" AE1200WHD-1A
I'm sure many would like to see a GShock in this category and if that's your thing, then more power to you, but there are already beaters listed above, and, frankly, I don't like GShocks at all. No, for digital it's got to be something more versatile. Something that can be dressed up just as much as it can dressed down. That's the Casio Casino Royale! I've had two and regretted neither. Both I put on a crocodile strap, notched to fit into the small lug span but have a little leather left beyond to flow with the wide case. Three main reason for this being the go to digital is the recognition and respect it gets among watch enthusiasts and the price! At that cost you might as well get a few and dress one up, one down and another to do some modding to. Oh yeah, did I forget to mention before... Great aftermarket support for modding these is available!!!