I've tried a handful of different films for 120, including 100 speed options. My style of 120 shooting is handheld without a tripod, and invariably, I'd end up in some situation when 100 speed wasn't fast enough or required a too narrow aperture for the subject. I'd also sometimes get confused about which film was in the camera (100 or 400?). I've settled on one film. Tmax 400. If I truly need a slower film, I have some filters I can use to cut down the light.

It's as grainy as a 100 speed film, but with the added speed. It's finer than tri-x. It can have different results with different developers. It's very versatile with different developers and isn't easily characterized by flickr or a single photographer's opinion.

The downside is it takes longer to fix, and is more "responsive to changes in development", meaning sloppy developing procedures don't produce consistency.