Toon Town opens an hour after official park opening, so you're going to be stuck at a closed gate. I have young kids and always start in Fantasyland (at least of late). If we are there at park opening, we ride Dumbo first because that line becomes a real long pain as the day wears on.
However the kids are growing and the last time we went we veered right. We encountered no line for Star Tours, got a FP for Space Mtn that was for 45 minutes later, rode Astro Orbiter w/ a 10 minute wait, saw HISTA, got FP for Autopia (good for 1/2 hour later), then rode SM and Autopia and did all this in two hours on a busy weekend day. The only draw in Tomorrowland is Space Mountain. The other rides are virtually empty until 11:00ish.
I haven't gone left in a long time, but I'd assume that with Pooh Bear opening and with PotC, HM, Splash Mtn, BTM and Indy, that part of the park draws more people. Granted there are six popular attractions to fill.
Depends on what you want to do, the age range of your group, and what you want to take advantage of. During 1st hour of any Disney day, you won't have too huge of lines for anything unless you're at DL during the week between Xmas and New Years. Then all bets are off--the crowds are obnoxiously huge and unfun. Got talked into going once. Never again!