I feel like MP7 is better all around. They are both great guns, but the MP7 can do things that the PP90M1 can't. For example, I killed somebody literally across the map without letting go of RT with the MP7. The PP can't do that. Then again, I feel like the PP is more powerful. Overall, I'm going with the MP7.
PP90M1 definitely has a damage advantage. Range on the MP7 does not mitigate that fact. I was shooting a guy from perhaps 20 meters with Range on my MP7 and it still took 5 hits to do him in. I don't think the difference with Range is worth it, as any SMG player worth his salt will stick to parts of the map where he won't have to shoot far.
MP7 with Attachments or Kick is best, as Silencer + Rapid Fire is an amazing combination and kick almost totally eliminates the already negligible recoil to the point that you have a literal laser.
I just got to lvl 74 yesterday. Used the MP7 for about 4 games so obviously I don't have rapid fire yet. That thing is pretty damn good even without rapidfire. I can't even imagine how beastly it is when I unlock it. The PP90M1 is my favorite SMG by far but this thing might just take over as the first gun I use my prestige token to unlock first prestige.