I've got three TLRs: a Rolleiflex 2.8F/Planar (which I paid only £350 for because cosmetically it's a beater, but the lens is in perfect shape--it is possible to find them at reasonable prices if you're going to use them to shoot with and not just sit them on a shelf), a Rolleiflex T with the 3.5 Tessar (found it in a second hand shop and paid £65 + a couple of old Zenit bodies for it!), and a Mamiya C330F.
I've been using my most recent purchase, the 2.8F, quite a bit recently to get the feel of it. It makes great photos, both in black and white and with colour film. The two main problems I have with it is that it does need a new/brighter focusing screen, and since I use it in the studio with strobe gear regularly, I had to buy a sync cord with the proprietary Rollei tip, as standard cords tend to fall out of the socket constantly. It is a bit lighter and smoother than the Mamiya, and a pleasure to use. I imagine it will be even more fun when I gather together the cash to get a Maxwell screen!
However, if I were first getting into TLRs, I'd go the Mamiya route (as I did). You can generally find good bodies at very reasonable prices, the lenses have come way down in price and are themselves superb, you have the advantage of interchangeable lenses--a huge boon--and as others have also pointed out, there's scads of accessories for them. And they're much cheaper, too--compare the price of a Rollei prism with a Mamiya, for a perfect quick illustration. Mamiya lens hoods are similarly much less dear than the Rollei items, and as you can use standard filters on the Japanese cameras they are considerably less expensive as well. Oh, and you can use regular camera straps with the Mamiya--I have an Op-Tech on mine. The Rolleis use a thin leather strap with unique alligator clips, so it can be difficult/expensive to find a strap, if your camera didn't come with one.
The Mamiyas, with their bellows, will also focus much closer on their own than the Rolleis. I've got a couple of Rolleinars for that purpose, but I'm not real keen on them, honestly. I've done some really good macro work with the C330F, a magnifying hood and a paramender, which is really not that difficult to use on a tripod.
So, I might give a *slight* edge to the quality of the Rolleiflex Planar lens--not that you'd notice it much in your photos, typically--and the camera is a bit lighter and possibly more finely engineered than the Mamiya. But in most other ways, especially versatility, I'd give the nod to them over the Rolleiflex, particularly to someone who is just getting into medium format/TLRs. They're wonderful for that purpose!