I used to use a G-Major for a long time, single space, could switch up to 3 amp channels, sweet delays, ok phaser and choruses etc.
Got my Boss GT Pro and never looked back...i don't even use clean randall pre's anymore, i use the Roland JC120 patch on it, THE BEST!!!!
I've had Line6 M13, but is terrible MIDI wise only has 48 scenes, instead of 128 like normal midi, terrible flangers and phasers, others tonally the best though.
I've had various units but none did everything in one like my BossPro.
My housemate has AxeFxUltra when they first came out and he has struggled with it forever, too many parameters, and once you turn up loud for stage, forget about hearing the same tone. Apart from that, it has no channel control functions, a terrible hum in the loop, the impedence for the input of guitar is not matched (i believe has been fixed on the new AxeFx) so your screwed for 4 cable method, and is overall horrible to quickly manipulate.
Goodluck dude!