I have not used either, but hopefully my input might be of some use.
It really depends on what kind of developer you are and your own
personality. I'm a recovering perfectionist, which means I'm
generally Type A and I lean toward being a control freak. I prefer
to do most things myself, so I typically don't go much for things
like InstantRails (or even Locomotive on the Mac). I don't really
like to use many plugins either as I'd rather roll my own stuff.
Hmm. Makes me wonder why I use Rails at all...ha ha.
Anyway, I'd say try the lowest level first (a la the book), then only
move up as it makes sense to you.