I like the rear one as-is. I'm running +1 on the front for easier cruising on the highway (lower rpm). It's must more popular to go the other way though (if you like a bit quicker start off the line).
If one is worn you should replace both sprockets at the same time (and likely the chain too).
In the rear: the more teeth you add, the faster you will accelerate. A very common change is +2 teeth in the rear for a total of 48.
In the front: The less teeth you have the faster you will accel. -1 tooth is very common. wouldnt go less.
I had the -1 in front and loved it. Just recently put on the +2 in the rear also. Only been down the road once. But its a wheelie monster even more now. Probably going to be good for the track.
I'm running -1 front +2 rear and love it way better than stock....the only thing thats kind of a drag is doing 85-90 on the freeway I'm between 8-9k rpms in 6th, but i got two bros slip ons and don't mind listening to the bike so it works for me :rockon: