Yes, heard all 3. My vote goes to the E Race. Half the price of the Akra (only mufflers though) and significantly louder. That said, I don't think it's over the top. The tone of the race is similar to the sport (beefy and deep) - just no valves to quiet cold start and a bit more volume overall. The challenge with the F10 is that everything is too quiet from the cabin...it's so well insulated.
The akra is gorgeous looking, hands down the best aesthetics. The sound is thinner, more mid range due to titanium. I think it's a very cool and unique character. It's just not loud enough - for that much dough it needs to stand out more. BUT when downpipes are added, it could be the perfect exhaust...I'm just speculating as I've no idea what high flow cats will sound like on the F10.
I'll likely be putting the axleback Eisenmann Race 90mm on my car very shortly.
Lastly, you should also consider the Meistershaft. That thing sounds wicked and has electronic valves to quiet the noise when you need to. I'm personally not a huge fan of the tips, but the sound is really nice. It also appears to have some legitimate HP gains as a full exhaust.
Best of luck. Whatever you choose will be a huge improvement over stock sound. Call IND if you want to discuss further. Those guys know their stuff