One item that I STRONGLY recommend is an adjustable axle. Also, get the trailer with the curved cross bar, therefore getting your boat closer to water level....
I agree with Andrew that not all trailers have adjustable axles, most seem to, but I have seen a bunch that are not and if you don't have the tongue weight adjusted properly it will suck to tow it etc... As for the curved bar, I totally agree with Andrew. I have one boat that does not have this and I sorely miss it since the launches I have access too limit it's usage and some of those really ducky areas have nothing more than a sand beach so you really might be screwed. LED's went on all my trailers last year, so tired of the old bulbs. I believe Harker talked highly of them a few years back along with others and now that I have switched I am sold.