Nato
Both are great boats, Don't worry about company stability, both have been around for a while and are well established.
As for the two boats the formula is going to ride better, but will be slower. Depends on what you want?
As for motors, I have the 500efi and love it, however if I was going to buy a new boat I would go with the 525efi, I really like the closed cooling on them.
WILL