I've compared the ARC LS15 and SP8 to the BAT VK31. I thought the BAT was generally fuller-bodied and a bit darker, though not lacking in air. I put some Bugle Boy tubes in the BAT and it's pretty hard to beat, now. ARC is good gear, but I think it's a little analytical for my taste. Obviously, these are not direct comparisons, but may give you some ideas.
