I vote 2008-13 M3. Great thing about the E90/92 is that it never went through a facelift so a 2008 looks exactly the same as a 2013 on the outside. And dat V8 doe!
Just make sure you compare operating costs so you know what you're getting into. An M3 is going to cost a lot more to keep up than an FR-S, and the initial purchase price is of course higher, too. You get what you pay for usually, but the FR-S does offer an awful lot of smiles per gallon!
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Current: 2005 Porsche 911 Carrera S 6MT
Previous: 2 BRZ's, 997 C2S, C5 RS6, C4 S6, B8 S4, GDB STi, S30 240Z, FC3S RX-7 TII, AW11/SW20 MR2, E30 318is/325i, etc.