id go with a marshall avt valvestate. those have the best sound in the price range of the other competitors. the mg series i find is way to metal sounding and cant get a good crunch tone out of it. i used a marshall avt50 for almost a year and loved it. i just had to switch to somethin with bit...
i prefer 4 12s. i know bassists seem to dig 4 10s more cuz its alot tighter sounding ..but for guitar it just doesnt do it for me. i like using full stacks altogether tho. :)