Jaime Lannister is easily superior to Brienne of Tarth. He was able to fight her to a statemate while he was chained up and malnourished. A healthy, two-handed Jaime Lannister would easily beat Brienne.
Of the show characters I'd rank them as:
S Class - Arthur Dayne
A Class - Jaime Lannister, Barristan Selmy & Robert Baratheon
B Class - Oberyn Martell, Gregor Clegane, Sandor Clegane, Khal Drogo & Brienne of Tarth
C Class - Loras Tyrell, Jorah, Bronn, Beric Dondarrion, Daario Naharis
I'm honestly not sure where to put Ned Stark. He is definitely talented and he was fighting Jaime Lannister to a standstill in Season 1 even though he was way past his prime and while he was losing to Arthur Dayne (not surprising at all), he was doing fairly well against him one-on-one.
