Note that I'm only going to focus on the original and classic (https://en.wikipedia.org/wiki/TGIF_(TV_programming_block)) run (https://tvtropes.org/pmwiki/pmwiki.php/Franchise/TGiF) on ABC from 1989 (https://www.google.com/search?q=TGIF+ABC+1989-90&sxsrf=AJOqlzWrsC2_Atrk1_Lf716ogJHfBo1qSw:1678949766098&source=lnms&tbm=isch&sa=X&ved=2ahUKEwizpp2j79_9AhWBZzABHe_QBwEQ_AUoAXoECAEQAw)-2000. Also, to keep things as simplistic as possible, I'm only going to focus on the fall line-ups and not any midseason replacements:
1989-90: (https://americantvdatabase.fandom.com/wiki/1989%E2%80%9390_United_States_network_television_schedule#Friday)

Full House
Family Matters
Perfect Strangers
Just the Ten of Us


1990-91: (https://americantvdatabase.fandom.com/wiki/1990%E2%80%9391_United_States_network_television_schedule#Friday_August_17,_1990)

Full House
Family Matters
Perfect Strangers
Going Places


1991-92: (https://americantvdatabase.fandom.com/wiki/1991%E2%80%9392_United_States_network_television_schedule#Friday)

Family Matters
Step by Step
Perfect Strangers
Baby Talk


1992-93: (https://americantvdatabase.fandom.com/wiki/1992%E2%80%9393_United_States_network_television_schedule#Friday)

Family Matters
Step By Step
Dinosaurs
Camp Wilder


1993-94: (https://americantvdatabase.fandom.com/wiki/1993%E2%80%9394_United_States_network_television_schedule#Friday_December_17,_1993)

Family Matters
Boy Meets World
Step By Step
Hangin' with Mr. Cooper


1994-95: (https://americantvdatabase.fandom.com/wiki/1994%E2%80%9395_United_States_network_television_schedule#Friday_September_9,_1994)

Family Matters
Boy Meets World
Step By Step
Hangin' with Mr. Cooper


1995-96: (https://americantvdatabase.fandom.com/wiki/1995%E2%80%9396_United_States_network_television_schedule#Friday)

Family Matters
Boy Meets World
Step By Step
Hangin' with Mr. Cooper


1996-97: (https://americantvdatabase.fandom.com/wiki/1996%E2%80%9397_United_States_network_television_schedule#Friday)

Family Matters
Sabrina, the Teenage Witch
Clueless
Boy Meets World


1997-98: (https://americantvdatabase.fandom.com/wiki/1997%E2%80%9398_United_States_network_television_schedule#Friday)

Sabrina, the Teenage Witch
Boy Meets World
You Wish
Teen Angel


1998-99: (https://americantvdatabase.fandom.com/wiki/1998%E2%80%9399_United_States_network_television_schedule#Friday)

Two of a Kind
Boy Meets World
Sabrina, the Teenage Witch
Brother's Keeper


1999-2000: (https://americantvdatabase.fandom.com/wiki/1999%E2%80%932000_United_States_network_television_schedule#Friday)

The Hughleys
Boy Meets World
Sabrina, the Teenage Witch
Odd Man Out

I liked 89-90. Although my favorite Also was pre TGIF with…

8:00pm Perfect Strangers
8:30pm Full House
9:00pm Mr. Belvedere
9:30pm Just The Ten Of Us

89-90

It just got slowly worse........

The 1993-1994 Season

1989-1990

89-90

It just got slowly worse........

I suspect that TGIF was really starting to run out of gas around 1997-98. It was around this time that Family Matters and Step by Step vacated the ABC in favor of CBS and their rival "Block Party" line-up.

In fairness, Family Matters was on its last legs anyway, it by that point, was for all intents and purposes The Steve Urkel Show. Meanwhile, Step by Step was having its own issues such as having to deal with the abrupt departure of Sasha Mitchell due to allegations of domestic violence and Brandon Call being on the mend after surviving being shot during a robbery attempt. And ultimately, Step by Step's final season on ABC came midseason.

With that being said, they were the two big flagship shows for TGIF dating back to 1991-92. And in their place (as well as Clueless, which was saved by UPN), were You Wish and Teen Angel. By this point, Boy Meets World was the only "normal" or "grounded in reality" show on the TGIF block. Every other sitcom including Sabrina the Teenage Witch had some sort of fantasy of supernatural premise. It just showed how essentially, interchangeable these shows were at this point. TGIF also made a similar mistake in 1990-91, when their entire Friday night line-up was made of nothing but Miller-Boyett produced shows at the expense of Just the Ten of Us. The short-lived Going Places took its spot on the TGIF line-up in 1990-91.

I think that it was also around this time that ABC following its purchase by Disney, attempted to pivot away from shows that the entire family could theoretically enjoy to pandering squarely towards teenagers/tweens.

I voted for '89-'90. Perfect Strangers and Full House back-to-back.

I voted for the 1993/94/95 lineup because it's the one I watched every week -- Family Matters, Boy Meets World, Step by Step, Hangin' with Mr. Cooper. The only one I watched from the previous lineups was Full House. After that, I also watched Sabrina the Teenage Witch and Two of a Kind, but it just wasn't the same.

In fairness, Family Matters was on its last legs anyway, it by that point, it was for all intents and purposes The Steve Urkel Show.
Oh, it was The Steve Urkel Show long before that. I still watched, and still enjoy the show. But I just went back and watched the entire first season on Hulu and realized what a nice change it was to have a straightforward family sitcom. Even the first half of the season (before Urkel arrived) compared to the second half (after he did) is a noticeable difference. The most irritating part for me was not just the "Urkel-Mania" but the various personas/clones and sci-fi "experiments."

93-96

Family Matters
Boy Meets World
Step by Step
Hangin’ with Mr. Cooper