If you're trying to decide between Range and Gideon: don't. You need both of them. Plan on doing both.
If you're trying to decide which one to do first, remember that Gideon is a more valuable toon but also requires more gear.
So if IT are a side project while you're also working on other things, definitely gear Range instead of Gideon.
If, however, IT are your sole focus, take this opportunity to do Gideon so that in the future when you're wanting that 6th trooper (for various reasons, including so that you can pair Piett with Vader), gearing up Range doesn't distract you as much as Gideon would.