If you notice, the Lakers bench has struggled. Farmar is inconsistent. Shannon Brown hasn't been as effective as he was in the regular season. Odom is on some night and off the next. I have yet to see of an NBA Analyst who thinks the Lakers have a better bench than the Celtics.
As for size, this is the exact same match-up pretty much from 2 year ago, except the Lakers have Bynum now. But Bynum is crippled, having his knee drained, and playing hurt.
The difference will be Artest and Gasol in my opinion. Everyone knows Kobe will get his. But I have noticed that Pierce struggles against physical 3's. He couldn't get off against LeBron due to his size. Artest is another very physical and big 3. I think Pierce could struggle.
Also, Gasol has improved in 2 years. He has a better feel for the triangle offense and is more acclimated to his teammates in LA. Plus, Garnett has aged in 2 years and is often hurt.
The Laker's Achilles Heel is their bench. If you watched the Thunder and Suns series (other than 1 game against the Suns), the Lakers bench often got outplayed and let double digit leads disappear. Look how many times the Suns came back.
In Game 2, the Suns came back to tie it after 3 quarters, then Gasol went off in the 4th. In games 3 and 4, it was the Lakers poor Bench play which allowed the Suns to take those games.
The Lakers should win since they are younger, have Kobe, and have possibly the best post player in terms of back to the basket post play in the league.