Nice ST, it'll cost a couple of grand to G/S-ize the ST, front forks and a longer rear shock.For me the G/S fork is crap and needs to be changed out anyway so even on a G/S one would have to change the fork..IMHO. I like the lighter and smaller G/S over the GS. It suits my needs perfectly.
+ it's a G/S
+ lighter weight
+ durability (monolever)
+ better off road.
+ good road manners (see note on forks)
- front forks are crap and SHOULD (IMHO) be replaced.
- front brakes weak but can take a larger rotor (+500)
- lacks power for two up touring
- weak subframe when using hard bags
+ two up touring
+ brake mod to four pot caliper $150 or less
+ better front forks
+ sub frame stronger.
- not as durable drive line ( driveshaft)
- heavier not as nimble off road.
If money on improvements isn't an issue the G/S is better IMHO, hands down....if you don't mind dropping the cash. If you have the ability to wrench on it for the modifications this can be fun. If not then besides the drive shaft expense the GS might be a better choice, especially if not going to push the bike off road.