How effective is an Archer vs. Mazzy (who has grandmastery in short bow)? What advantages would the Archer have?

I wanted to try an Archer (maybe not as my main character, but possibly a 2nd PC in a multiplayer setting) but I haven't used Mazzy either and I've read some good things about her on this board.

Archers are really powerful, if missile weapons is your style ( i prefer melee) cos they can get loads of attacks per round and a really low THAC0, and have called shot. Mazzy is a powerful fighter cos she has bonus abilities like edwin and haer'dalis. If you prefer missile weapons go for the archer, if you want a good short sword player go for Mazzy.

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Haladar
Mithril Cavalier of ALSB
Guardian of The Holy Temple of Aerie

don't bother with an archer; mazzy works just fine. by the end of SoA she's (or any other fighter with bow grandmastery) down to an archer a 1/2 attack and an insignificant amount of THAC0 and damage (+3 mb, but all THAC0s below -10 are pretty much equivalent). she has great saves and her innate improved haste more than makes up for any combat deficiency. besides all that she can actually be useful in melee if needed (17 STR, not limited to just one slot in melee weapons, not restricted to studded leather armor > all penalties of an archer).

I strongly suggest an Archer PC. I haven't tried Mazzy myself, but I doubt she could come close to a PC archer. My first main character was an elven archer, and by the end of the game, he had about 60% of all kills in the party, even when I was grouped with Minsc and his celestial fury. At higher levels, he's rarely ever hit. With the right proficencies and equipment, they can become quite fearsome indeed.