Here's something I wrote for another forum with a very similar question:
Getting the right size and using the correct sized plates are more important than brand. Padded straps don't mean shit if the carrier isn't for you. When getting plates, they should cover from your jugular notch to just below your rib cage in the front and from about C6-7 to T8-9 in the back (I run back plates a bit higher than pictured due to greater threat from elevated positions and to allow more mobility). See picts below:
Once you figure out what size plates you need, you can pick your carrier size. Large plates won't fir well in a Med. You can run Med plates in a Large PC but they may shift a bit. It's not uncommon to run a med PC with a Large cumberbun. It's better to run plates a tad small rather than too large. Too large of plates will restrict your arms forward movement, espetially when pushing forward with a pistol.
How often and what you intend to use the gear for will determine what price range. Condor/Voodoo stuff is cheap and good for the occasional class but don't expect it to hold up to routine use. You do get what you pay for. My LBT 6094 costs about $400 but I can load it down and run with it all day long, every day without it moving around. My JPC cost less and is a snugger fit however it sucks with more than 15-20 lbs on it. Stick to well reviewed (reviewed by shooters, not air softers) kits like SKD, Mayflower, Crye, LBT, VS, etc...
Trying some on and out is the key. While this may not be easily done at the local gun store, finding some locals at the range who can let you try their kit out will help you make better decisions. You'll find that 1 PC can't do everything you want. Mission drives the gear...I have 4 different PCs I use frequently depending on the mission.
Regarding types of plates-do your research. Hopefully Mick-boy will chime in with some of the articles he's written about ceramic vs. steel. I've worn ceramic and steel (with and without backers) and I prefer ceramic every time. Thickness isn't as much as an issue for me as is weight and protection level. If you're looking to protect your life, don't go cheap. If you're looking for range/training stuff then look on armslist. (I've seen ESAPIs for less than $200 there)