Cree is the brand of chip the led's use and is generally considered to be the best. I ordered mine cheap off ebay and they get beat up pretty bad in the salt water and open air storage and they still work great. I have them on my 15' aluminum duck boat.. 24" combo beam on the front, two 6" - one on the stern pointing back and one on the motor hood pointing forward (lights up the inside of the boat like high noon).
Some things to look into IMO are:
The ability to stay waterproof with prolonged exposure to weather and salt water/air.
Spot/Flood combo for the bigger bars. You'll be surprised how much area a flood beam will cover.
I will say that if you're using it on a boat, bigger is not always better as the high humidity in the air will reflect the light right back into your eyes (like high beams in the fog). Wal is right though.. If you can mount them up high like on a t-top the big ones will work much better.