you probably won't find any tube amp for much less than $600. let me go back and change up what I said earlier......one of these type amps you had listed would probably be ok to learn on. granted, it won't be like a tube amp. and you'll probably want a tube amp one day. but you should get whatever you can afford right. I would still recommend looking at the Vox Valvetronix amps over what you had listed though.
the downside of a tube amp, is that to get that "right" sound, you have to have the volume cranked. and if you're just learning to play at home, that would be unbearable to anyone else in your house. so in that respect, a solid state amp is the right choice because you can play at low volumes and many of them have headphone jacks.
so yeah, look at the Vox and maybe the other ones you had listed. I don't personally like the Roland and LIne 6, but they'd be good enough to learn on.
