Here are my two favorite episodes from each season:

Season 1:

Angels in Chains
The Séance

Season 2:

Little Angels of the Night
Antique Angels

Season 3:

Mother Angel
Terror on Skis

Season 4:

One Love, Two Angels
Of Ghosts and Angels

Season 5:

Angels of The Deep
Angel on The Line

Sorry, but it's too tough for me to pick just two, so I'll pick three...

Season 1:
"Angels in Chains"
"Angel Trap"
"The Mexican Connection"

Season 2:
"Angels in Paradise" (Cheryl's debut)
"The Sandcastle Murders"
"The Sammy Davis Jr. Kidnap Caper"

Season 3:
"Angels in Springtime"
"Mother Angel"
"Counterfeit Angels"

Season 4 and 5:
Only saw each episode once or twice over 35 years ago. I don't know enough about them, so I can't claim any favorites.

SEASON 1:
Lady Killer
The Séance

SEASON 2:
Angels on Ice
Angels In Paradise

SEASON 3:
Angels in Springtime
Haunted Angels

SEASON 4:
Angels on the Street
Angel Hunt

Season 5:
Angel on the Line
Hula Angels