Cannot decide first family trip on or off site!!

[isla bonita]

HELP!! There will be 5 of us... Me, hubby, son 10, son 7, mother-in-law.
I keep reading and reading and reading these boards and can't get away from the "magic" everyone talks about from staying on-site!
I know it seems to make more sense staying off site but will I regret not being in the "magic?"

How's there magic with the MIL? Sorry had to throw that in the mix> LOL

I am sure it will be lovely.