I have a custom built Tikka in 6.5 Creedmoor that started life as a TAC-A1, but I ended up overhauling it over the years to be a full PRS competition setup. I swapped out the factory trigger for the Timney T3 2-stage trigger and it's excellent. I heard the KRG Midas trigger is also very good, but I don't think you can go wrong with either. The Midas does have some fitment issues so I don't think it works in a TAC-A1 chassis, but any other stock/chassis should work fine.
IMO the factory triggers on Tikka rifles are really good, in fact they're better than most factory rifles especially with the trigger spring upgrade. That said, the Timney and KRG are both better in feel, adjustability, and offer lower weights than the factory trigger. I've had a great experience with the Timney and have managed to bring home steel from matches. Don't think you can really go wrong with any of the options discussed, just depends what you want.