I've been to a GNR concert last year in Prague. Axl sounded fine, I haven't heard Jon live since 2013, so I'd go for Jon. Performing wise though Jon > Axl. Axl was a bit static, left the stage often during jams and solos while Slash and Duff were the heartbeat of the show as they were amazing full of energy!

GNR show as an overall was a great experience for me and I would definitely pay to see them again! Worth the trip on a bus from Greece to Czech Republic