Well, first of all, medium format offers more diversity than any other area in photography.
Way more diversity. There are medium format SLRs, RFs, TLRs, view cameras of every type, you name it. So take a tour if you can- try to get some gear in your hands and get a feeling for what will help you feel productive when you use it.
I know this isn't practical for everyone, but when I first got into medium format, I tried literally a dozen or so cameras of all sorts. And actually I never settled on any one particular camera- they all have particular strengths. So I wound up keeping more cameras than I probably should have
Their specialized abilities are what made them attractive to me. So... as of now my most productive medium format cameras are 6x7 SLRs and 6x6 RFs.
I am not sure why big old TLRs tend to come up as people's favourite starters, I find them very limited for most of what I do, but everybody's mileage varies.... so definitely try them and try everything you can.
If you like the Mamiya RFs but the price tag was too high, consider the older fixed lens Fuji RFs. Similar ergonomics and ease of use, fantastic level of detail, but much lower cost. Look at the GA645W in particular, that one is good fun. The GA645Zi is now overpriced in my opinion, it's is a lot of fun but the price has gotten a bit ridiculous. I mean, the zoom range is rather narrow. I had one and a 645W and used the latter more than the Zi. The older folders are fun too but don't base your impression of medium format performance on those, most of them are not up to par with what you can get from their nonfolding cousins, notwithstandign the pricey bessa 3.