Proportional has a nominal fee of 3%
PPS has a nominal fee of 10%
By nominal, I mean if the pool's luck factor is right on, meaning the same as the current difficulty. If you look at the difficulty history, there have been times in the past where the pool took, on average, 11% more time to mint a block. Under those circumstances, the miners who are using PPS are coming out ahead. More often than not, however, deepbit does a little better than average, so PPS would be doing a little worse. The rule of thumb generally is that if you are going to be mining 24/7, proportional is the wiser choice. If you are going to be mining on and off, or gaming while mining, you may never get a share in during a round, or perhaps only get a couple of shares; this is where it is wiser to use PPS.
Just to sum it up; with PPS, no matter how well or how poorly the pool is doing, you get a fixed rate, but come out at about 10% less than you would solo-mining. With proportional, things should equate to about 3% lower than if you were solo-mining.
At your 105MH/s, the difficulty would probably change many times before even finding a block on your own, so that is where joining a pool is beneficial; you get stable micro-payouts.