Towering Indrik rates 160th overall, and Trestle Troll is just behind it at 166th. They rate 45th and 50th among commons, respectively. Obviously Towering Indrik is just a clone of Giant Spider, which I think tricks some people into thinking it's not very good. Trestle Troll is new, and noticeably different, so it intrigues drafters. But which one is actually better?
First, let's say what's not different. They're both 4-toughness creatures with reach. They're essentially the same mana cost, with Trestle Troll rolling a little bit cheaper because mana-fixing is pretty prominent in RtR (Guildgates, Keyrunes, Axebane, etc).
Now, how are they different? Well, Indrik has that extra point of power, which kills Runewing, Vassal Soul, and an unleashed Chainwalker. It also kills any Guildmage that attacks, which reduces them to basically artifacts. And those are all cards you're going to see in opposing decks in drafts.
Trestle Troll has a different appeal. It's more suited to sitting around taking beats. The regeneration option is fairly reasonably priced, which means he can block over and over again if you need him to. He's well-suited to green decks (Golgari and Selesnya) where you need some time for your plans to come together.
There's one more feature of Trestle Troll that complicates matters slightly: Defender. In most sets, this would be a flat negative, as Indrik can serve a more versatile purpose if the board allows; the Troll has to stay back. But, in Return to Ravnica, there are two common cards that specifically benefit from having a large number of defenders, most importantly the aforementioned Axebane Guardian. Trestle Troll helps you speed up your ramping as well as providing a sturdy blocker to hold off your opponent while you work towards that eleven-drop Worldspine Wurm.
This decision is razor thin. As with some other potential discussions, a lot of it is going to come down to the rest of your deck. But in a vacuum, I think that extra power and the ability to attack is better than the regeneration. The possibility of the card working with other cards isn't enough to overtake Indrik.
Joe's Pick: Towering Indrik