Apart from a slight bump in processor speeds for the base and higher configuration models, there isn't anything different.
I would get whatever suits your needs at the price you can justify. If you can get the base Early 2011 model for a good price and that will fulfill your needs, then that's the one you should buy.
If you need the fastest 13" MacBook Pro available, then buy the Late 2011 model.
Whatever you choose, remember you always save money when you upgrade the RAM and SSD/HDD yourself.