As Marie13 and runsongas have already brought up, you need to provide more information about what you are planning/hoping to do. More info allows people to give better advice.
I will say this from the advice side. Read people's comments but remember that most everyone is going to suggest what works best for them and what they prefer. There will be a variety that should indicate that what works best is not simple. I am sure all recommendations will be for gear that is quality and has a proven history.
Because of this try and find an Instructor, and/or a Shop, that has a rental option. You need to figure out what works best for you and trying multiple options is the best way to do that. Finally, please get an Instructor if you were not already planning on it. 100's of dives create a bank of knowledge on how to tweak/adjust/set up Sidemount gear that makes the process so much nicer and more fun.
Edited to add: I use a XDeep Stealth, Apeks XTX50's, and both AL80 & LP85 depending on gear and water temps.