When you throw synths in the mix, everything changes!
For straight guitar in, I'd recommend the Pod HD500X, unless you can afford an AxeFX. The Pod also gives you the option to use the JTV guitars at a later stage for the ultimate combo package.
I've used the HD500, Lexicon MPX G2, MP-1, MP-1C, MP-2, Rockman XPR, Nobels SST-19. The HD500 is easily the most versatile and more modern of them all. The others may have better tone in some cases, but the Line 6 computer interface puts the HD500 in another class altogether. Best ease of use on stage.
Now if you want synths, all of the above is out. The Roland G5-55 requires a 13-pin GK equipped guitar for best performance. It has now been trumped by the Boss GP-10. However none of them track as well as the Fishman Triple Play (FTP), which requires a separate hexaphonic pickup on your guitar and a computer or iPad to make the sound. Tested well on stage, but requires higher technical knowledge.