The modeled guitars on all the JTV models are the same (with the exception of the 89 having a model of its magnetic pickups in one of the Custom banks per the latest update). I think any difference between the way the modeled guitars sound on the different JTV models would be very minimal. In a blind test, I doubt anyone could tell the difference.

Al, I have both a JTV 69 and 59P.  My 69 is a first prodution Korean, old model tremelo, 1st string spacing issues on neck/nut/frets.

If I had to have just one, it would be the 69..  the reason is the tremelo and the SSH magnetic pickups as a backup.

I use the modeled sounds 95% of the time, but some times I use the mag pickups during a song to move from an acoustic model to a chime or lead tone.  I have an HD500 and have presets for Eagles/Boston stuff where the preset sets the JTV for 12 string (and a PA patch) and another for a Boston tone JTV Les Paul HB bridge and lead HD500 patch.  On the fly changes of the JTV are great.  The 69 SSH pickups and 5 way give a good quick alternative.

The tremelo is not that great but OK (touch wise and tuning stability), but I need that for surf tunes.

The 59P is a great instrument (and more appropriate for the Jazz/Classics soft stuff I play at my weekly gig..  People see the GT 59P and see a 'tame guitar' vs. the strat 'look'....  Tone wise they are pretty much the same model tones wise, the 59 does have better sustain (and some strings ring much more with sympathetic sounds than the 59....this is commented to on this board).

So, the 69 is more versatile for me.  I play both (but at different venues).