Nothing wrong with the S400 and just as accurate as anything else, and probably the most common gun as mentioned already.
The MPR version is the best version of the 400 and easily as good as the HFT500. The HFT500 is a touch longer which puts me off a bit and I would go for the MPR over the 500, but if it feels ok to you then its just as good. The FTP is very nice, but very heavy even though it doesn't feel like it, and you might find it a struggle to start with on standers. As you get used to shooting you will find weight is your friend.(gun not body).
Money no object then I would go custom stocked MPR or a Steyr.
The main issue is really gun fit with the stock and the balance. Try before you buy go to the club with Chris, he's a rubbish shot but knows his guns.