The basic version is called "Pro". It comes with 200 MIDI styles (out of 1700 total). There are lots of jazz MIDI styles in there, maybe 50 or so.

In terms of realism, the "RealTracks" styles are much better sounding, because they are actual audio recordings of top musicians. For example, in the jazz category, the bass part is typically played by Neil Swainson (George Shearing's bass player), Drums by Terry Clarke, guitar by Oliver Gannon, piano by Miles Black. Or for Smooth Jazz, you have Elec. Piano by Jeff Lorber, sax soloing by Eric Marienthal (Chick Corea's sax player).

In terms of jazz only, the Pro version has these 2 "bands"
Jazz Swing 140
Medium-Slow Jazz Quartet 110

In terms of jazz only, the Mega version has the same bands as the Pro version, plus these additional ones:
JazzBallad 85
Jazz Bebop 190
Jazz Waltz 140
SmoothCool Jazz 100

THe UltraPak has over 600 RealTracks, compared to 70 in the MegaPAK, and 20 in the Pro version.
The UltraPAK has about 200 Jazz RealTracks (200 Country, 200 Pop/Rock).
Compared to the Mega, the UltraPAK has many more jazz styles (Ballad 60, Bossa, Gypsy, more Smooth Jazz, Modern Jazz, more soloists etc.)
You can hear the Jazz and other RealTracks demos here http://pgmusic.com/realtracks.audvid.win.htm

So, as an overall answer to your question: the Pro version would be a great starting point for someone learning jazz. You can use RealTracks for your swing tunes (since you have 110 and 140 RealTracks, they should work well for swing from a wide tempo range (about 70 to 190).
As mentioned there is a 30 day MBG. As well, you can upgrade to a higher package within 30 days and not lose any money. For example, if you get the Pro version, and then wish you had got the Mega instead, you can update to it for the difference in price.

Have Fun!
Peter Gannon
PG Music Inc.