If you are looking to upgrade from the Studio 8 software than you should upgrade your hardware as well. here are some reasons why:
1) Studio Deluxe hardware was made for Studio 8 software and does not work too well with other programs
2) The prices of software programs like Premiere are not too different when purchased alone or as part of a hardware bundle. Adobe gets $500+ for Premiere but you can buy the same software with the RTX100 or DV500 hardware for $499
3) Realtime! Even if you get the Studio Deluxe to work you will not get realtime editing capability
That being said, the "best" software will depend on what you're looking for. Feel free to give me a call at 800-323-2325 x110 and I'll be happy to make a recommendation... and perhaps some of our previous customers will do the same on these boards!