I gotta ask ya, Zombiekiller... what do you want to do with it? Are you looking for a fun plinker, or a target gun, or a cheap trainer for a handgun you own?
I ask, because I haven't been real impressed with the Mosquito or P22. The P22 was very reliable, and it was fun, but it was very small, and limited to plinking by the short sight radius and small size. If a toy's what you're looking for, the P22 would be my pick. I tried a Mosquito (I carried a P229 at the time, was looking for an inexpensive way to practice) and felt it was built too cheaply to say "Sig" on the side of it. It had a few feeding issues, but I mostly disliked the feel and quality of it (admittedly, my expectations were high).
The above said, have you considered a MkII or MkIII? Here's my MkIII 22/45, I love it:
It's plenty accurate, plenty reliable, and a hoot to shoot.
DO make every attempt to try out the P22 or Mosquito first, so you aren't disappointed.