My choices in order of preference would be
1) FS1R
2) TG77
3) TX802
4) TX7
In answer to your question the TG77 is a more advanced FM engine ( AFM ) than the TX802, has the AWM waves as well and has effects. The TX802 has no effects or AWM and has less FM algorithms. Plus you can find a lot more sounds online for the TG77/SY77. There are a lot of DX7/TX7 patches available you could use to build patches for the TX802 but you would have to set them up yourself.
[This message has been edited by Nigel (edited 12-11-2005).]