Grand Livina really isn't spacious and is more of an estate car with rear seats than an actual MPV.
Innova has got the ruggedness of the Toyota IMV line-up, with a more forgiving ride than, say, the Fortuner. 2.5 D4D engine isn't fast, but if you only want a strict people carrier, this is the best choice.
I personally like the Carens more, but be warned that at full capacity, it's probably as low as a Genesis Coupe. The plus side though is that at normal operating conditions, this has a better ride than the Innova. And the best part, for me at least, is its engine. Its CRDi can shame those boy-racers in open exhaust Civics and Corollas.
For me, if you need a rugged yet refined vehicle that's strictly a people carrier, it's the Innova. If you want something with a bit more flair, it's got to be the Carens.