My prayers for something without RHD have been answered!
Obviously, nobody is going to claim changelings deserve +1 LA, or are too weak for +0, so I won't go into detail about their abilities and traits. They got a decent chassis, a unique and versatile ability, the option to sneak their way into race-exclusive material, and one of the best prestige classes in the game is semi-exclusive to them, so there's plenty of reasons to play a changeling even when the more powerful +0 LA races are on the table.
I'll also use this post to remind people that MM3 isn't a setting-specific book, and changelings therefore aren't either. Use that knowledge wisely.
+0 LA, as stated before.