Agree with the posts above, Atwood and Barker are two good brands and both have a big following.  My new trailer came with an Atwood.
Basically, you just hitch up your trailer on the ball, unbolt the old jack, install the new and hook up 2 wires.  You can download the instructions for Barker and Atwood to review first.
Like other said, you should the standard 3 bolt configuration which is all I've ever seen btw on travel trailers. One difference in the models offered by Atwood and Barker is if you go with the higher poundage rating, you get longer travel on the jack.