Depends on whether your buying new or used.
The new triumph is meant to be a corker. It will cost less to run in servicing costs too. I found the previous triumph very soft power-wise, and not that great on the handling front either.
I found the ST3 a little underpowered. For reference I would say it has similar power to a Honda VFR800, but handles a lot better.
Personally I'd go with an ST4S. This has the 996 engine, and goes just as well as a 996, except with a comfy seat
If you want to save some money you can get some tremendous bargain on second hand STs. There is/was a 3 year old ST4S on ebay at the moment with a starting price of 3k5 !