Hi Ed, you may have noticed that more GSs have ABS than not. It's generally considered to be a desirable option, will make the bike more marketable if/when you come to sell it, plus of course give you the benefit of anti-lock braking every time you ride.
Have a search of the site for more opinions, as not everyone considers ABS a no-brainer option for bikes (and the GS in particular) as it is with cars. The 1100/1150-era ABS was still a bit crude, and adds a cha-chunk noise to the general 11xx GS cacophany when it arms itself as you set off. It's also rather sensitive, and a bit of wee can escape when it kicks in unexpectedly on descents if you hit a pothole, patch of gravel, manhole cover, pile of horseshit etc. and the bike suddenly lurches forwards brakes-off for a fraction of a second (although it feels a lot longer) Most of the time though, I find it reassuring rather than worrisome.
On ABS-equipped bikes, you can disable the ABS on the rear wheel when you start the bike, for offroaders who like to plough a braking furrow with a locked back wheel on descents (or just do skids)
The ABS also provides you with a helpful early warning of when your battery's dying, by not arming when you start the bike.
HTH and hope you find a GS to love