I can't speak anything about either gun but I will say the atlas magazines are hands down the best 2011 mag there is.
STI mags, meh, they kinda work and the cost isn't that bad.
Mbx, yeah f*#k that trash and f*#k the dude who makes them.
SV, hit or miss for the price. Some last forever and some split just like mbx.
Get atlas mags with grams guts and don't look back!