You gotta consider the pros and cons and decide yourself.
If you stay on 5.1.1 all your JB apps and tweaks are already there and work fine and you dont have to do much or wait for upgrades to be released to work with the new firmwares JB.
If you update to 6.1 you will be at the latest possible JB firmware version and you will have all the 6.1 features plus you wont have any problems installing or updating any appstore apps that need ios 6.0 and higher.
Most major cydia packages will be updated to work with the new JB ios version but that can take time and you might have to deal with bugs and glitches.
Decisions