Well if you all fit in the TT you'll all fit in the Brera.
Reliability - I've had my Brera 2.5 years, no problems. There was a faulty Bosch sensor right at the beginning but that was sorted swiftly and nothing since. The Breras are really solid, nothing to worry about (except the occasional issues with diesel DPFs and EGRS that seem to bother all marques).
Engines: that VAG 2.0T is a great petrol engine, however the Brera 1750 turbo petrol is coming out this year and will be kick ars* - it'll either be a 200bhp single turbo or a 235 bhp twin turbo. If it's 235 it'll be to die for. The weight is low on the turbo model as well. Even the 200 will be great.
The Brera 2.4 Diesel is a great diesel engine (if you like diesels), if you want diesel then get the Brera over the TT.
Looks: TT is desirable but I still don't like the side view and not sure about rear view (like the light clusters though). The TT is a bit ubiquitous though. Brera just stunning and quite rare - gets treated like a supercar, so many people turn and look at it.
It's all subjective but if you do fancy buying a Brera I seriously doubt you'd regret it.
Brat Pack no.8