Kubik,
Glad to see that you're interested. I think it's something of a SIN that the C64 is represented (very well) on the XBOX, but its arch rival is not!
Personally, I use ZX32, simply because I'm familiar with it, and when I started using it all those yeasrs ago, it was by far the best....
However, I don't think that you can go far wrong with ANY Spectrum emulator. The fact is that on the PC they have been working on such emus for years and the Speccy hardware is so archaic that it has been very well 'seen to'. There are even emus that boost the sound and add extra colours!
Anyway, the attached list should help, and includes direct links to source code where available! I'd encourage you to go for it as, if nothing else, you could have the Kudos off knocking out the first Speccy emu on the XBOX - no-one could ever take that away from you. And with a huge back catalogue of superb games available, given all the other emus already available, this really would be my next emu of choice. ANYWAY, try the below link and see what you think!
http://www.void.jump.../emulators.html PS If you need any help in terms of documentation/beta testing or compatibility/FAQs then just shout - that is more my bag than actually coding....
The link below gives you some idea of which are most popular, by listing the number of folk who have downloaded them!
http://www.worldofsp...g/emustats.html