I'm a fan of Akra and I would suggest it because it would be easier to upgrade to a full system later (can add the Akra Evo mid-pipe more easily). Plus there are many available used and it will be easy to sell in the future if/when you move on to another car.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - Ohlins TTX, Fall-Line Suspension Arms/Bushings, AP Racing BBK, OE GTS Aero, Cobra Seats, Akrapovic GT4, GMG 4-point, BBS E88