Titans, being the 20 RHD outsiders they are, are very hard to assign a LA to, if only because of the sheer number of abilities they get. To somewhat simplify things, I'll be comparing them to balors, those other 20 RHD exemplars of chaos.

The most obvious difference is size: balors are Large whereas titans are Huge. In terms of ability scores, titans definitely come out on top. Their land speed is higher, but they can't fly like balors can. Natural armor is equal. A titan's SR is 4 points over the fiend's, but has no energy immunities or telepathy and worse DR. Balors also have slightly stronger natural attacks, as well as much stronger special weapons.

Magic-wise, I think balors are better off as well compared to the kinda weak list of SLAs titans get. The titan's stronger 1/day abilities are more than compensated for by at-will True Seeing and Summon Demon, in my opinion (unless your DM allows Gate cheese, in which case all bets are off anyway).

All things considered I'm not sure I'm convinced the titan deserves +0 LA. -0 and +0 both seem possible: for now I'll go with +0 because it's still a versatile and strong ultra-outsider.