#9 "The Watchers"(Season 2)
I liked this episode because it introduced Joe Dawson, another great character. It also introduced the Watchers, a group of mortals who have been observing Immortals for centuries.
#8 "Unusual Suspects"(Season 6)
If you're into mysteries you'll like this episode. It's 1929 and Hugh Fitzcairn has been "killed", only he doesn't know who has done it. MacLeod shows up and tries to solve the mystery but his list of suspects keeps getting shorter by the minute with the people being killed by the killer.
#7 "Black Tower"(Season 6)
A sort of Highlander meets James Bond episode. Duncan is in a building with everyone wanting to kill him. He can't leave though without saving his date who is trapped.
#6 "Brothers In Arms"(Season 4)
I liked this one because they showed us some of Joe's past. It also brought us the death of Charlie and why the Watchers and Immortals have stayed apart for so long.
#5 "Methos"(Season 3)
It introduced Methos, need I say more?
#4 Two-part "Finale"(Season 3)
Yeah I know they're two episodes but I'm still putting them in the same slot. I liked how this episode was written. If it had been written that the secret was revealed to the world then that would've made the series a lot more....well...interesting.
#3 "One Minute To Midnite"(Season 5)
Watchers and Immortals almost at the point of war against eachother. Not much could top that.
#2 "Timeless"(Season 4)
This is without a doubt one of the favorites of just about every Highlander fan. This time Methos is the one to get the girl.
#1 "Comes a Horseman" & "Revelations 6:8"(Season 5)
So I have a problem with splitting up two-parters. This is my favorite part of the series. Duncan MacLeod against the Four Horsemen, which includes Methos. But thankfully in the end Methos turns on the Four Horsemen.