I'm at L5, and I've found a lot of success in a zerg rush of troopers. Here's the loadout I use to get 100% on almost all of my attacks:
- 46 troopers
- 2 med droids
- 4 X-wing
All maxed out at L5. I don't attack mortar farms, because they tear me to shreds, but there are plenty of Imperial bases that are easy kills. If there are any mortars, I drop Leia and a med droid in first to take out the hardest point of the shields, then take out the mortars with my X-Wing. Then I follow her with 23 troops, and drop the other 23 and a med droid on the other side of the base. If there's a droid hut or something out in the corner I'll drop one soldier there to take it out. Since turrets only target one soldier at a time, this gives the rest of them plenty of time to take it out. Most of the time I finish a match with 30 seconds to spare and at least half my troops still alive.
I like this combo so much I haven't leveled up to 6 because I don't want to mess with a good thing - it's got me in the top 10% on the tourney, and I expect to finish higher than that once it's done - 100% on every battle gets you up to the top quick.