As you can see from above, the choices are endless. Skipp the Holga its junk. Also dont forget you will probably need a MF film scanner of some sort.
At first i think it depends on how you like to shoot, and that depends on tripod, handheld, etc etc. Portraits or stilllifes. Landscape or snapshots and although you might know the subject you like to shoot you dont know which MF camera is best for you to take those shots yet.
The format question should come first. Do you want 645, 6x6, 6x7 or 6x9.
Probably the next step is to decide what type of camera fits me and what do i shoot. Rangefinder, TLR, SLR, older RF (very manual) and go from there.
On the SLR side, ask, do I want a TLR or a SLR type camera ?? and decide if you want to frame through a prism like with a Pentax 645n, or pentax 67 (like a giant 35mm camera) or if you prefer a chimney finder, like a hassy style where you look through the top. One thing to remember is a non prism chimney finder camera like a hassy, the image is flipped from side to side. Drives some people nuts.
Once you figure all that out, you will be close.
The main types are......
Rangefinders - good for landscapes and low light shooting, but framing and close up shooting is not that great. Great for backpacking. Not so great for portraits, product, still lifes etc.
Most of these modern cameras are light. The fuji GA series has AF and AE and autowind. The GA645ZI is like a giant P+S MF camera with a 3 step zoom lens. There are also the Mamiya 7, Mamiya 6, all the fuji 690's too. Also there are all the older cameras like the Mamiya press, 2x3 crown graphic etc etc. The Fujis have fixed lenses except for some of the early RF cameras. Too many to list really.
The top of the line of these is probably the latest interchangeable lens Mamiya 6/7. Probably the best deal for the $ is the Fuji GA645 cameras, or the early Fuji 690 cameras, but the early 690's are very heavy. Maybe the Bronica too.
TLR cameras - Probably the best all around for low light and accurate framing, due to the dual lenses. No mirror slap, etc. but they can be heavy. Also these are chimney viewfinder cameras and usually have fixed lenses.
All of these are totally manual cameras as far as I know. The top of the line for these is the Rollei's. Probably the most versatile are the interchangeable lens Mamiya C220 and C330 cameras.
Great low light anything camera where you need accurate framing.
SLR cameras - Of these there are several styles.
The first type is like the Pentax 645n, or pentax 67. Those are like giant 35mm cameras with a prism. The 645N is auto everything, if you buy AF lenses. The 67II has auto aperture exposure only. There are a few of these type cameras around, mostly in 645. mamiya 645, Contax Bronica and maybe a couple of others.
Of these probably the top would be the Pentax 67II, Pentax 645nII, Contax There are quite a few top cameras in this area.
Probably the best deal is an older Pentax 645 or older mamiya 645.
The second type of SLR is the chimney finder type like , Hassy, Kowa, Mamiya RB/RZ, etc. some of these you can buy angled prism finders for so you can shoot them normally from the back. You can get a chimney finder for a Pentax 67, but no rotating back.
Within this chimney SLR group there are 2 types again. Some of these cameras like the Hassy 501 have internal focus lenses. Some have non focusing lenses and bellows focus like the RB/RZ and Fuji 680. Something like a Pentax 645 type slr is easier to shoot handheld. The bellows cameras are better on a tripod and much better for macro photography.
The best of these are the Rollei 6008, Fuji 680, Hassy, RZ.
The best deal in this area is probably a Kowa 66/super 66/66m, a Mamiya RB (bellows)or a Bronica. Also to me something like a Kowa 66 is easier to shoot then a Mamiya RB.
If you managed to wade through this long winded post you can see there are an awful lot of choices out there. Actually too many to start, and the only way to know what will fit you is to start renting and shooting cameras.
Also you may want to go here and read a lot and especially read the Danny Gonzales overview. It has a lot of good info.
Dead Link Removed
I think the first step is choosing a film size depending on your enlargement requirements. The next logical step is to choose a RF, TLR or SLR.