Spin-offs are easy. Spin-offs are hard.

Spin-offs get to use pre-existing characters from popular shows — or, at a minimum, get to introduce their new characters on a pre-existing show — and therefore have an easier time getting the audience's attention than some wholly original concept. But spin-offs also remove those characters from the context where people first liked them, and they can be unfairly held to the standards of the original show, whereas a brand-new series is only judged for being itself.

And it's hard to know exactly what kinds of spin-offs will succeed, creatively or commercially. Frasier Crane worked spectacularly well away from the gang at Cheers, while Joey Tribbiani seemed much less lovable once he was 3,000 miles away from Chandler and the other Central Perk regulars. "The Simpsons" far outstripped the popularity of "The Tracey Ullman Show." Sometimes, audiences instantly take to characters introduced to a pre-existing show for the sole purpose of spinning them off, like that time "The Danny Thomas Show" stopped in Mayberry, or when the lawyers from "JAG" ran afoul of some NCIS agents. At other times, characters introduced for spin-off purposes vanish without a trace, like Jess's estranged dad in a never-produced "Gilmore Girls" spin-off, or that eccentric private eye who was investigating Dr. House for a while.

Some hits prove unusually conducive to spin-offs. "Happy Days" (which was itself technically a spin-off of "Love American Style")  produced both two of the best spin-offs ever in "Laverne & Shirley" and "Mork and Mindy," and one of the worst ever in "Joanie Loves Chachi." "The Mary Tyler Moore Show" not only generated other hit sitcoms in "Rhoda" and "Phyllis," but somehow turned Lou Grant into the lead of his eponymous drama series. Other hits like "Seinfeld" never even tried.

That's the double-edged sword "Better Call Saul!" is facing when it debuts on AMC Sunday night at 10. As a prequel to "Breaking Bad," it's going to get much more attention than a wholly new show about a sleazy lawyer would, but it's also going to be constantly compared to one of the greatest dramas in the medium's history, which is perhaps more burden than a light-hearted legal drama should have to shoulder.

For what it's worth, I liked the first few "Saul" episodes, and Vince Gilligan and Peter Gould had some smart things to say about the show. But before it debuts, the HitFix staff picked some of our favorite — and least favorite — spin-offs of all time. It's an eclectic bunch, including "pure" spin-offs like "Frasier" and "Joey," more calculated ones like "The Andy Griffith Show" and franchise extensions like the "Star Trek" shows of '80s and '90s. If nothing else, the list below suggests there's no one right or wrong way to make a spin-off, but treating it like a show that has to function whether or not anyone has ever seen an episode of the parent show certainly helps.

So take a look at ours, and then sound off in the comments on some of your most and least favorite spin-offs.

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com