There will be no difference in risk of bacterial infections with oil based or water based gear assuming the quality control of each UG lab preparing the products is the same.
There are 5 main causes of PIP:
first the shorter the ester, the higher the melting point. The shorter the ester - the more PIP
second, the concentration of the gear. The higher the concentration - the more PIP
third, the solvents used. The more BA - the more PIP
fourth, injecting too quickly
fifth, virgin muscle.
Long estered steroids that aren't highly concentrated are pretty much PIP free. I would stick with things like testosterone enanthate, tren enanthate, testosterone cypionate, primobolan depot etc.
Stay away from things like T400, test prop, tren ace etc.
Here are some additional tips for reducing PIP:
1. Heat up the oil prior to injecting. Run the vial under hot water for 1-2 minutes. Heating up the oil will bring it closer to body temperature and make the oil disperse from the muscle into the blood stream much easier.
2. Gently massage the injection site for 1-2 minutes after the injection. It'll help disperse the oil into the blood stream.
3. I am a big advocate of training the muscle you injected into that day. It'll help disperse the oil from the muscle into the blood stream. In other words, try to time your glute injection on the day you train legs/glutes.