I think it depends on your prefference and what kind of conditions you will be running in. If you plan to run a BIG lake with lots of chop the magnum 57 is the way to go. The Manta ray is good compromise between the two. I like the Magnum myself, but the manta ray is nice also. check out this review of the mantaray
http://www.rcboatmodeler.com/reviews/mantaray.asp
Let us know what you decide.
Happy Harvick