Depends on how many weaps.

For 2, I would just assign a single key (or mouse action) for next weapon, since you already know what the next weapon will be.

For 3 weapons, I would assign a key for weap 1, a key for previous or next weapon. That way you can quockly switch to any weapon in 1-2 easy to remember steps.

For four weapons...I would just assign a key to he first and 3rd weapons, and get to any weapon in 1-2 clicks. (assign a next weapon button too).

Personally never tried 4, but it seems like a logical setup. Then again, my custom controls only use the mouse for aiming, so you'll have to play around with settings to find out what works best for you.

Gaming mouse can have 5 different controls on top of usual aiming method..

A more ergonomic one can cost ya, but the extra controls can be extremely nice and useful for games with a few more actions than (normal finger/hand reach). And if you're playing long enough to get hand cramps, considering one is not an option anymore. You can either pony up now, or when the doctor tells ya you have carpel tunnel at the ripe old age of 22 (like one of my friends).