Westco is good. Motobatt is as good apparently and likely cheaper.
Before you change the battery, you have checked the terminals are tight and the charging light on the dash is not lit? If that is okay then I would do a few tests on the battery & charging circuit first, which can be done with a cheap multimeter. 3 readings will tell you a lot. Static voltage in the battery without the engine running, 12.5V okay. Voltage with the engine running, lights off, 13.5-14.5 okay. Voltage with the engine running & lights on, 13.5 okay at idle, rise a bit if you open the throttle.