Hi,
5083 is generally considered a marine grade, it is not as strong as 6061 but has pretty fair corrosion resistance. You need to approach with care when
machining, it can be 'sticky' and result in Built-up-Edge. Coolant and lubricant reccommended.
6061 and 6063 are both very readily available and have a good balance of strength, corrosion resitance, machinability and weldability. There is a reason
that they are so popular.
There are higher strength heat treated and work hardened grades like 2024 (aircraft grade), but rare as rocking horse s****t and pricey.
Tooling grade 7075 has come down in price as it is used much more widely than it used to be. Great strength, good machinabilty only fair
corrosion resistance, and weldable only with full solution heat treatment.
Craig