Season 1: Support Your Local Mother
Season 2: Where There's Smoke, There's Rhoda
Season 3: The Good-Time News
Season 4: The Lars Affair
Season 5: Will Mary Richards Go to Jail?
Season 6: Chuckles Bites the Dust
Season 7: The Last Show
It's hard to pick one. Some of these episodes are tied with others for first place
Season 1: Second-Story Story (some people are Bob Dishy fans, I'm a Bob Dishy fanatic)
Season 2: Some of my Best Friends are Rhoda
Season 3; Farmer Ted and the News
Season 4: The Lars Affair (even though I was so frustrated that we didn't even get a glimpse of him!)
Season 5: Menage-a-Phyllis
Season 6: One Boyfriend Too Many (because we got to see both Mary's old beau and new one, Dan and Joe)
Season 7: The Critic
I could easily pick several more as big favorites including any episode that Nancy Walker appeared in or the first season episode with the adorable Paul Sand as the guy from the IRS who audits Mary.
I'm curious as to why you picked the ones on your list.