leaf spring vs. torsion axle? 14" vs 15" tires?

I've researched aluminum trailers .... got a list of 2 dozen manufacturers but found one that actually has decent pricing. (which I'll be posting soon).

I'm in the market for an all aluminum (frame and box) 6x12 v nose with side door and double barn doors in the rear.
(ramp door costs more and I like barn doors)

the trailer I found had single axle leaf spring suspension .....
I'd rather have tandem torsion if it's an option that won't break my budget.
It's gonna cost more ....
but just why do I want it?

oh, btw, I live at the beach and my last trailer, steel frame with aluminum box rusted into dust ..... all except for the aluminum parts ..... I want all aluminum this time!