I'm mainly a metal keyboardist that also plays guitar sometimes.
I use currently an epiphone les paul with ampkit on the iphone, and it's great to practice at home or in the studio.
It happened that I'm starting to play with a band (trash metal mainly) so i was thinking to upgrade to hardware and was having a look to multifx and ampsim pedalboards.
My attention has been focused mainly on 3, line6 xt live, digitech rp500 and boss gt8.
What are the main differences between them? Best effects, best amps, easiest to program, most flexible....etc.etc.
I've never once heard a GT8 sound anything other than terrible. (No offense to those people that use them)
If you're looking under ~$500 USD, the Pod HD 300/400 are probably your best bet, and the L6 M13 seems to get pretty positive reviews as well:
[VIDEO]http://www.amazon.com/Line-6-M13-Stompbox-Modeler/dp/B00181ER7C]Amazon.com: Line 6 M13 Stompbox Modeler: Musical Instruments[/VIDEO]
I had a Digitech GNX3 once upon a time, and you can get them extremely cheap these days. It wasn't amazing but it certainly wasn't bad. Here's one for $130 USD.
Digitech GNX3 Guitar Workstation Multi-Effects Pedal PD-5771 | eBay
I don't know anything about the RP500 or the XT Live, but the XT is old tech for Line 6, so at least go with the HD. Stay away from the Boss.