Does anyone know which lm is the best version to upgrade to? I have an old version and it's working well but keep getting the message to upgrade.

Which version are you using now?

What OS are you using?

If you're still using LW 4 then you'll find LW 5 way different (& not necessarily better). Use the forum search to look for update or problems update or something similar - you'll probably find a heap of threads

Also check out the LW changelog to see what's been changed in newer versions: Changelog - LimeWire

Just remember that if you're using an older Pro version & haven't renewed Pro - if you update then it will be to the latest basic version. And if your Pro installer isn't saved then you'd lose the Pro version completely