For a new player, I advise experiencing the content on the way up. There are plenty of great old story arcs and one off missions to experience, and other than story arcs and badge missions, there are a lot that you can't flashback (some that award various temp powers as well). Plus, with story arcs, running them as they become available has the advantage of not limiting your teaming options as you progress (flashbacks lock you into TF mode, meaning once started, you can add others to the team)
I am actually running several characters that have not taken any double experience at all, some to hit various arcs and other missions as they level, and a couple others hitting all the TFs or SFs on the way up. Roc and Roll just hit 41, and is the one hitting all the TFs. He just did Market Crash, and now to get caught up, needs Hannon, Quarterfield, and Moore. I am hoping I get those knocked out before the L44 TFs come up. Been trying for days to get a Hannon, and no luck whatsoever (don't have it unlocked myself) Going to try again after this little late 4:20 break...