I have a 1.9TDI I have a custom exhaust system with twin tips (Looks amazing, well I think it does.)
However the oval tip is gorgeous also.
If its diesel and your going for a stage one remap just have a straight through pipe, No back box and no cat.
If your looking to go stage 2 and beyond (Clutch, new turbo etc) then I'd recommend a sports cat as you can get alot of smoke on stage 2 and I'm told sometimes fail emissions