Just me, but I'd skip a half frame camera. I had a Pen FT for a while, but didn't use it much. 35mm is already stretched for quality, and 72 frames on a roll for me means that it tends to sit a lot.
Lately I've been using my Leica M3. It's maybe the best built camera I've ever handled. I've mostly been using it with a 50mm f/2 Summicron dual-range and a 35mm f/2.8 Summarit, but it's just a dream to use. Leicas are a deep rabbit hole to go down, though, so don't necessarily look at that. Rangefinders in general have their own quirks and learning curve, and old Leicas like the M3 have to be vetted carefully because they're prone to problems like desilvering or prism separation that can make the rangefinder patch difficult if not impossible to see. The M3 also adds an extra layer of fun as the viewfinder covers the area of a 50mm lens, only, so you either need a secondary/external finder to use something wider than 50mm, or use a lens with auxilliary optics("goggles") to change the viewfinder coverage. I have the latter on my 35mm lens-it looks goofy but works.
One of the things I'd caution is that there's a lot of junk out there.
Unless you just really want a point and shoot, I'd avoid that and opt for an interchangeable lens camera of some sort. Most P&S cameras weren't that great, and the ones that were bring big money these days.
The big thing I'd be really cautious of is 70s and 80s consumer-level electronic heavy cameras. They tend to work great until they don't, and repairs are a nightmare. I've ventured inside a few, but they can be scary as a lot of the electronics are on flexible circuit boards that are now very delicate/brittle. The Canon A series cameras, including the AE-1, AE-1 Program, and A-1, are notorious for this. t kills me to say that I consider them a bad idea in 2024, considering that my first "real" camera was an A-1that I still have and have used the snot out of, but honestly they were built kind of cheaply to begin with and time hasn't been kindest to them. I'd also avoid Minolta X series. Even pro cameras like the Nikon F3 and Canon New F-1 have some of the same ills, but they tend to be a lot more reliable...with F3s especially though, if your heart is set on one, well change your mind
(I don't like the F3...) but also don't be tempted by a broken one. I fixed one once and amazingly it still works, but it was a mechanical issue with the shutter timing.
I'm a Nikon guy now and have been for several years, and I have owned at least one of every film SLR body Nikon except for the FM3a. I refuse to pay the prices they still bring-it was one of Nikon's last new film cameras and had a fairly short production life, and for me I actually consider it inferior to the FM2n(the FM3a basically is a kind of FM2/FE2 hybrid-the FE2 has aperture priority AE but is battery dependent, the FM2 is manual only with a 3 LED meter, and works without batteries. The FM3a is aperture priority with an FE2-type meter readout but can also work without batteries).
Here's kind of my general guidance:
1. If you want mechanical/manual focus, there were some great suggestions above especially in the FM and FE. The FM is all mechanical with a meter that reads out using 3 LEDs-it was quite high tech at the time, but is simple and intuitive to use. The FE is aperture priority(and of course manual). I don't like the meter read-out as much as the FM, but it's still easy and straightforward to use. The FM2(and FM2n) and FE2 are newer/"improved" versions of the FM and FE. The big differences are a a 1/4000 maximum shutter speed, up from 1/1000, and the flash sync speed improves from 1/125 to 1/200(1/250 on the FM2n). I have a preference for the FM2n, but there's also a big jump in price from the FM to the FM2 and if you're just getting into this, it's honestly probably not worth it.
Someone did mention the Nikkormat. I'm reluctant to suggest these for a few reasons, even though they are built like tanks. There were a bunch of cameras bearing the Nikkormat nameplate. Ignore the FS, which has no meter and really is more a collectors item now. The FT is a pain as you need to manual tell it the maximum aperture of the lens mounted. The FTn does this semi-automatically by twisting the lens to minimum aperture after mounting, but it's dependent on no longer available 1.35V mercury batteries for accurate metering. The FT2 can use much easier to find LR44 type silver oxide cells. The FT3, which is uncommon, works with AI(auto-indexing) lenses.
Of course don't overlook the pro bodies. The F2 IMO was a high point for Nikon, and it remains one of my favorite cameras, particularly the F2SB and F2AS versions. The F2A is a great option if you want an F2, and they are not that expensive. I love the Nikon F(I actually just bought yet another today-I think I have about 15 of them now) but the F2 fixes a lot of ergonomic quirks that the F has, including adding things like a swing-open back for film loading.
Most anything else is great, but there are two specific models I'd avoid-the EM and the FA. The former was Nikon's lowest end camera at the time it was introduced, and essentially is meant to be used only as an auto exposure camera(aperture priority). It has only very, very limited manual controls(you can select the flash sync speed, 1/125, manually but that's it). The FG succeeeded the EM and is a great and often overlooked camera(I'd personally avoid the FG20, which is more or less just a cheapened FG). The FA might get some controversy from Nikon faithful, but I'm still salty over mine with an intermittent fault that causes random blank frames and that I can't track down. I have another that I think works fine, but what's the saying-once bitten, twice shy? It's a shame too as it's a technically impressive and very capable camera.
2. If you want something modern with auto film advance, autofocus, etc, first of all, I'd suggest just chopping off the bottom end cameras like the N55, N65, N75, N4004 etc. The N70 is a bit of an oddball and I kind of like it, but the controls definitely are on the unconventional side and not the easiest to learn.
Among these, I'd stick to the advanced amateur/semi-pro and pro level bodies. I actually kind of like the N80, which also has really good compatibiltiy with modern Nikon lenses, but watch out for broken film door latches. The N8008 is great, y but IMO I'd skip it and go to the N90, which is similar but has somewhat better AF and plays nicer with new(er) lenses. The F100 is probably the bang-for-buck stand out in this bunch, just like it was the hottest camera of the year when it was introduced in 1999. Autofocus is nearly as good as the F5, lens compatibility with old and new is great, and they honestly are pretty reasonably priced these days. I love the F4, but it's a polarizing camera and not necessarily one I'd recommend going out to buy. The F5 is great, and more affordable than ever, but it's a beast that eats 8x AA battereis like they're candy. The F6 is wonderful, and if I wer going to only keep one 35mm SLR it would be tough for that to not be the one I'd pick, but the F100 gives you probably 90% of what the F6 offers at 1/5 or less the price.
That's just my suggestions and thoughts from someone who has WAY too many cameras...
And BTW, just since I love looking at it as much as I love using it, this has been my kit for the past few weeks. This was the only camera I used on a trip last week. I'm no longer using the meter shown here-I'm using a Voigtlander VC Meter II