I think the tides have started to turn back, xrumer use to be the only good option apart from custom made solutions (selenium, phantomjs, slimer etc)
But xrumer went quite, the world started using honeypots and such, anti-pam APIs became really dominant, and GSA started to become more significant
I think the tides have started to turn back again, people are starting to pick up xrumer again after it's release with xevil2.0 and it's ability to detect honeypots
People have also become more savy to API's, using clean IP addresses and not doing any posting, waiting until they've reached enough sites, then often just doing account linking rather than posts / content.
Xrumer also uses a js engine of sorts now (not sure how), GSA does not, so Xrumer gets by many of the js antisplam detection that GSA gets caught by
I think xrumer is a little more advanced than GSA for bypassing antispam (not by much), GSA is more popular right now, if xrumer can solve this no-captcha-recaptcha it will once again shoot ahead of the competition