My opinion.
There are various discussion topics.
My principal interest is technical and hardware.
One of arranger keyboard�fs targets is human-like automatic back-up band.
Various approach:
 Style Structure
 Real audio integration
 Real-time control
 Sound sample reality
 Etc., etc.�c

In the style structure aspect;
Korg�fs more chord variation is unique
approach.
JammerLive�f random selectable multi riff
is very interesting.
Gem�fs more riffs is interest too, etc. etc.

But, there is no champion.

Long measure per riff ;
Korg and Gem specify max. 16 measures per
riff, but I am thinking it difficult to
compare because it depends on memory
capacity and style compression rate what
most makers not specify.

Sometime Korg has more than 16 measures
riff.
Soft developer of Korg seems creating
longer measure style than other maker.

To have all merits in one product is impossible. More hardware capacity means more product cost. User�fs feedback concern of musical effect / cost analysis of each approach is important.

In this discussion, top arrangers grouping possibility is very interesting.
I vote on Roland group chord variation capacity , because I can�ft use complicate chord or rootless chord play style.

Riki