You shouldn't be taking on more than one person at a time unless they're very weak or a pair of snipers or something. Get the pick, hide, reload, and then continue the onslaught. Whenever I killed you instead of moving forward I went in a circle, which gave me time to reload and pick up health/ammo before making another assault.
And yeah, demomen are really satisfying to kill because it's not too hard but they're dangerous if they see you coming. Snipers are the easiest to wreck, and pyros can be easy if dealt with correctly but are one of the top threats to a scout (along with soldier, heavies and sometimes other scouts). If you fight them in a tunnel you're usually screwed unless they're W+M1 scrubs. Then you backpedal with your pistol.