First, MF film is harder to load onto any reel than is 35mm film, in my experience. The extra width just makes it hard to get the film properly centered to start the operation.
That said, I've never been able to get 120 film loaded onto my AP or Paterson plastic reels. The ball bearings that help with 35mm film just seem to interfere with MF film, which doesn't have the edge perforations of 35mm film. My favorite reels for loading MF film are plastic reels with a couple different Russian tank designs. There's a
current eBay listing for one of these. This tank is nice because it takes less fluid than most tanks. It uses a plastic reel that loads like a Paterson reel, but without the ball bearings and with a smaller diameter. The downside is that this style of tank only supports rotational agitation, not inversion agitation. I find it's tricky, but not impossible, to get it right; too much agitation produces streaks, and too little produces underdevelopment. Get it just right and the results are great, though. Overall I don't like this tank too much because I've ruined too many rolls because of the tricky agitation, although it's relatively easy to load the reel.
The other Russian tank design is uses reels that are similar to Paterson reels in size and shape, but they lack ball bearings. I've got a plastic Jobo reel (without a tank) that's similar in this respect, although I've never actually used it. I therefore expect that the Jobo reels would be easier to load than the Paterson reels.
I've got both 120 and 220 stainless steel reels. The 120 reel is relatively easy to load, but it has its quirks -- it's hard to center it properly, and when it's not properly centered, the film tends to skew off and jump the grooves when loading. Once centered, though, it loads fairly easily. The 220 reel is similar in this respect, but it's easier to get the film to jump its grooves -- I've only loaded this reel successfully a couple of times. With both reels, I tend to get crescent-shaped creases in my film from mishandling when loading.
Overall, I'm planning to use my second Russian tank for future MF endeavors, since its reel gives me the fewest problems. If it breaks, I'll get a Jobo tank to go with my Jobo reel. (I'll probably try the Jobo reel in my Russian tank -- I know it fits -- at some point.)