I've had painted, galvo, and Trailex. The painted ones are no good after a few years of fresh or salt water. They just don't hold up. Galvo are much better, but will eventually rust, especially in salt water. The aluminum is by far the best for a few reasons.

1)Weight. My trailer for my TheMightyHobie18 with the axel, wheels, and tires shipped to me with a weight less than 200 lbs.

2)Corrosion. Aluminum trailers will not rust. The only problem I have is with any glavo hardware attached to it. i.e. the bolts used to bolt the thing togeather. They may need replacing every decade or so. This depends on how well you wash the trailer down after submerging in slat water. If you sail in fresh they will last as long as the aluminum.

3)Ease of attaching accessories. The extruded aluminum pieces have a track on at least 2 of the faces of each piece that accept T bolts. You can bolt almost anything you want on them without haveing to drill holes in your trailer.

4)Longevity. They will probably last longer than your trailer.

These are just my opinions, but if you plan on being in the sport for a while, I would invest in one. Especially if you will sail in salt water.