It all depends on the ramps you use. The only advantage I can see to the aluminum float-on type is less weight and possibly faster loading IF you're not by yourself. On some ramps, they don't allow powerloading. The disadvantage is potential for water in the bearings and need to check them often.
As Ken said, with a good roller trailer and a power winch, you can launch anywhere, anytime, by yourself! I personally prefer the EZ-Loader design. They use aluminum shafts, and nylon bushings in the rollers, so NO lube is required! They use so many rollers that the load per roller is only about 150 lbs, and the design is such that all rollers balance against each other, insuring even load distribution. The cross members are designed to rotate as boat goes on/off trailer, providing a "tilt trailer" function without the sloppy tongue/frame joint common to tilt trailers. Bought my trailer new in 1985 and it's still going strong 25 years later! The only thing I've done to it is change the rollers from black rubber to urethane to eliminate black marks on the hull. The washers and hog rings do tend to rust but I bought stainless washers for mine and coated the hog rings in grease to eliminate that problem.
Note that only the TIRES get wet! I've only pulled the hubs once in about 25 years and they were fine. The 16.5" wheels don't spin very fast and the bearings never get wet so they'll last a long time. I believe a well designed roller trailer requires LESS maintnance over time, and allows you to launch at virtually any ramp.