My first film-Camera was a EOS 3, because I use the EOS-System and thought it would be a good a idea to get a fullframe camera. My digital camera at that point a was APS-C-based camera. After a few rolls, I sold it. Than I got a ZEISS NETTAR 6x6 folder. After developing the first roll I started loving MF. Since the ZEISS NETTAR has no light metering or focussing-system I wanted to have a camera that included all this. The Contax 645 found its away to me with 3 lenses: 35mm, 80mm and 140mm. At this point, I learned a lot more about photography and stopped worrying about ISO and so on. At this time I got my tripod and loaded with Velvia 100F this camera was fun - I think it was the best SLR I ever owned. During the Photokina 2012 I played a lot with Linhofs and Sinars and all the GF-stuff and soon I decided to go for a larger format. But this decision was difficult and as a result I sold my Contax 645 and got a Mamiya 7 with again three lenses: 43mm, 50mm, 80mm. I'm addicted to 21mm in Smallformat or 90° of view. The Mamiya 7 is not as advanced as the Contax 645 is, but it has a larger format and good (excellent) image quality.
The decision to switch to 120 was pretty easy for me. 120 gives me a lot more image quality. The size and weight of my equipment negligible for me.
Keeping in mind, that one roll of 135 Provia 100F costs 10.70€, one roll of 120 Provia 100F about 6€, a pack of 5 rolls 29.50€. I usually buy packs of 5 rolls.
With my Mamiya 7 I get 10 shots per roll. You could say, that 10 shots is few compared to 36 shots on 135, but in landscape photography 10 shots is just enough for one scene including some exposure compensations. So I can finish my work on one scene and change rolls more often and this lets me change my setup for each scene. With 135 and 36 shots the film remains much longer in the camera.
So 120 is not cheaper in the costs/image ratio but in the costs/area ratio. Im also more capable of dealing with the lesser number of shots.
EDIT: My only 135 camera is a Contax G2. I won't sell it because for me it is a unique camera. I wish Canon would learn a few things from this camera, especially looking at the EOS M