Although you can make the srt4 faster for less money... once you get the money the mustang will kill the srt4.
So if you're looking to keep the car for a while, and eventually spend some money on it, go with the mustang.
If you're just looking for quick, cheap performance that you're gonna sell in 5 years, go with the srt4.
And yeah, the mustang is better looking and a nicer ride than the srt4.
Personally, I'd get something used. Probably a mustang.