IMO if you can stretch the budget the GT4 is the car to get, it looks really cool yet a little still understated, and should depreciate the less, but then will also tie up the most money.
However, if you are not going to track much then maybe the GTS is better. The turbo engine will handle the long manual gearing better at lower speeds due to the wider torque band. Then if you tune it you'll have up to 440hp or 490hp with E30 plus masses of torque with both tunes. In terms of performance this might make the GT4 feel a little boring on the street and a good driver will leave the GT4 behind on the track. Alternatively the GTS 4.0 might give you that flat six sound you've been looking for but when you put an exhuast on it it will sound pretty raucous and might give you a headache. Whereas the 2.5t sound is quite muffled and subdued on the street, you could say more civilised. I would say the value proposition at the moment would have to be the 2.5t GTS.

Totally agree. With a decent corner exit, a 718 GT4 is not pulling away by much if at all. A GT4RS on the other hand... 😬

I'm still getting used to it, but the 718 2.5 tuned platform has good manners on the track and doesn't suffer from a lack of power. This was from my first weekend in the car.

Great lap, great lines - nice work Chris!

For the OP - you'll note that the powerband is pretty wide with the torque produced by the turbo engine. This is a real benefit on the street since general drivability is excellent and dropping down a gear to get some oomph isn't needed. On the track, it allows for using a higher gear than you might need with a normally aspirated engine - resulting in potentially less shifting events per lap. As @DonR wrote, if you can swing a GT4 that's a great option. But at a substantial discount a GTS turbo (or well equipped S) may be the sweet spot for your budget.