I have the Line 6 JM4. In addition to a real easy looper interface it has all the amp sims and effects that you would normally find on a Spider amp. Basically turning any amp into a Spider IV. It also has an impressive assortment of jam tracks. A nice feature is that when you select a track the looper automatically assigns a complimentary pre-set tone to play with it. Of course you can change keys, tempo, etc. It's also loaded up with a gazillion genre/artist pre-sets.

They call it a looper but it's really more of a Line 6 amp + amp sims + processor with a looper feature.I think they're selling for a smidge over $300. I've never used any other looper so I don't know how this one "measures up" but I can't imagine a looper being any easier to use? The only thing I DON't like about it is that it doesn't have an on/off switch ! You have to physically disconnect the power cord from it to turn it off. How hard would it have been to add a power button!?

Good Luck