Well, I had a really long post typed that I somehow lost so here is a summary.
My local four Winns dealer has this chart on their site to show you what your vehicle can pull.
http://admin.pagelite.ca/ocadmin/download.php?itemID=1140Here's my opinion from past experience:
Basically if you are only going to pull your boat back and forth to the lake and you need to maneuver tightly then go with a single axle. But.. buy the disc brake option, they work better and are easier to service. This assumes you have a big enough vehicle to pull the rated load. I have pulled my H200 two hours away with no problems on a single axle trailer.
If the combined load is over 6,000 lbs then go for the tandem or if you are a little light on the tow rating with your vehicle. Buy the disc brakes on both axles. But you need extra room to maneuver a tandem. You can't just jack-knife the trailer to get them pointed where you want because you will screw up the alignment on the front axle.
I know you will never know all the spots you may go but I would think you will develop some favorites that suit your application really quick. I have several ramps around here that I won't go to again.
Be sure and buy a spare tire, good quality low profile hydraulic jack and a 24" or 36" breaker bar with the appropriate size socket to remove the lug nuts. I also carry a couple of pieces of 2 x 8 and 4 x 4 for jack support and to prevent the trailer from rolling backwards. Also remember that a tandem has four tires to replace when it comes time and you get more drag so they are a little harder to get moving (more fuel?).
Good luck and I hope you make a good informed decison.