Trust me, before you buy either one of those guns look at the Springfield XD series. Cheaper, just as reliable and plain fit your hand like a glove which is the most important part. At least try one. I was so surprised when i went to buy a new Glock that i ended up with the Springfield.

that being said, either of the guns you mention are good. I have had the luxury of shooting both. The P99 was a little bulkier then the glock. The glock was a little cheaper. Both shot good groups when i did my part. If you are stuck on these two guns, jsut buy the one that feels best. The reason you are buying it is to protect yourself. You have to feel comfortable carrying it, and holding it. No sense in buying something that doesn't fit you.