Yes he used a ball and chain
*not* a "flail" type weapon, an actual heavy steel ball on a chain he'd launch into English ranks as he charged to break them up

he'd probably have worn chainmail, as he was actually a man of minor station (accounts claim his uncle had been high sheriff of Lanark before the English removed him from that position) and later of high station (Marshal of Scotland) and could afford such
whether it would have been the expensive and life-saving double linked chainmail that was developed to protect the Crusaders I don't know (was Mediveal equivalent of Kevlar as it could stop even bodkin arrows unlike normal chainmail)
the use of targe (Scottish shield) and a heavy cutting broadsword is also likely (NOT a basket hilt sword as they were much later creations)
there's an episode of World's Deadliest Warriors where an expert demonstrates with a Claymore, lopping through three (dead) pigs' necks in one go (equivalent to a Human's neck), showing how damn fearsome the claymore was :flamethrower:
If you want to get realistic though, the Roman gladius was the best damn
soldier's weapon until the advent of breech loading rifles, claymores etc required too much room to swing, could lop off allie's arms easily, took lot of effort and wore you out fast
gladius you just stabbed easily, aiming if possible NOT for guy in front of you, but for guy hititng your mate to your right who wouldn't expect such, same tactic eventually broke the Jacobites at Culloden when English troopers used their bayonets against the Highlanders to their right as they couldn't defeat them face to face with any good chances.
So I like the Imperial sword in Skyrim

note: Scotland consists of a lot more than just the Highlands, Wallace was not a Highlander, but from near Glasgow
he was believed to have worshipped at the 11th century church (goes back even further than that but parts of the 11th century building still stand) in my town as some his family lived nearby in Lanark

http://www.scotsfamily.com/wwallace.jpg
"ALBA GU BRATH!"