Should I save my SP for Marines instead of buying Sentry Planes?

I have 537 SP right now, with Helicopters and Submarine upgrades.

Yes buy marines, if you don't play world games then you'll not use sentry planes much.

Yes, don't buy Sentry Planes as rank 2.

before you buy anything consider how you would like to play.
on the one hand if you like for example stealth units then buy the strategy Guerilla Warfare,...
on the other one if you are a fan of bombers wait till you can buy Sky Menance,...
of course there are much more playing styles and upgrads, so just consider your way and then decide (any high rank will probably advise you what do buy, just ask one)

Thanks!

Another tip:
MoS=rich areas only (europe,NA etc.),depending on your country if it's a 10000 funds game (play it whereever you want on 15000)
GW=almost everywhere,even africa if you want

Save up for mos or gw