You might as well ask which caliber handgun is the best.
You will get MANY opinions on boats.
We've had 2 Regals and now have a Sea Ray. Each were in the class you are looking at (19-21 ft., ski/water fun). Both Regals (19 footers) had MerCruiser V6 IOs. I put S.S. 19 pitch props on both. Both were excellent boats for water fun (tubing, wake boarding, skiing).
The Sea Ray is a 21ft with V8 (5.0) MerCruiser and Bravo Twin Screw props. I haven't skied behind it yet, but it is a noticeably heavier boat and I can tell the gas usage is going to be more $$. I can also tell it may need the lower pitched props for the out-of-the-hole shot.
I have looked at the build quality of many boats over the years and some I would NOT own are Maxum, Tahoe, Bayliner, but just like guns/ammo ...opinions will vary!
EDIT TRIVIA: That first Regal (1985 model) could pull a 200 lb male slalom skier up easily...with FOUR other adults in the boat! Best boat for skiing I have owned!