If your new, stick to NiMH, There's a LOT of research you have to do before even considering using a LiPo battery. They require higher maintenance than NiMH due to the fact they can be quite dangerous.
And although some manufacturers state their guns are "LiPo ready", it's a blatant lie. If a gun doesn't have a fuse, it's NOT LiPo ready. And you still have to choose a battery with an appropriate constant drain rating (the C rating)
Give these two threads a read through, it should be everything you need to know about LiPo!