I would say that the idL, while more expensive than the Tama-go, it's much more fun, and in color! But, it's kinda like a 'anything you can do I can do better' thing between them, with Tama-go having a park, but so does IdL. But, as I said, IdL's are quite expensive, so it would really depend on your budget.
Tama-gos are great and cheap! Plus it is a lot of fun if you buy figures. But I have never had an iDL they might be a lot of fun too. (Just kinda expensive.) If you can afford one I would go for the iDL.
I choose idl. Tama go is cheaper than idl. But Tama go is so boring. I had a Tama go and when I played it about 3 months, I'm getting bored. Idl had fun features.