Snaps are better than straps (or bungee cords) for sure - but snaps still do break apart every once in a while.
Bungee cords can scratch your boat and allow to much ballooning to occur which can tear your cover. Ropes or straps get loose (stretch) and cause ballooning as well and can be a pain in the but to untie if they get really tight.
I'd say Snaps would be the best choice with a custom cover if you can swing that in your budget.
I would also get a repair kit - I bought a snap install tool and it's good to keep in the glove box as it seems the snaps come apart in the middle of long road trips.
https://www.amazon.ca/Seasense-Faste...nvas+snap+tool
The new Lund/Crestliner fitted covers now have "J hooks" that slide into place on the groove in the rail - so no more broken snaps yet you still get a tight custom fit travel cover.