Katy Perry to guest star on 'How I Met Your Mother.' How do you think she'll compare to the others?

Sorry. No How I Met Your Mother guest star will ever surpass Alexis Denisof, who first appeared on the show in 2006 and returned last week, as No. 1 in my heart. No one. After him, every other stunt casting has been but a minor blip on my I’m-still-not-over-Buffy radar. (I’ll get over that soon, by the way; I swear. Just let me, um…)

The good news for Katy Perry, who will be appearing in an upcoming episode as Zoey’s (Jennifer Morrison) “naïve and beautiful” cousin, is that the spot for No. 2 is still available. There’s tough competition, though.

I was a big fan of Rachel Bilson’s guest stint on the show, and Joe Manganiello was hilarious as Marshall’s law school buddy Brad. (You could argue that the two were recurring characters, but let’s not get into that.) So if Perry wants to put up the good fight — and I’m sure her goal in life is to earn a respectable place on our arbitrarily ranked mental lists — she should study those stars’ appearances on the show closely.

Your turn, PopWatchers. What do you think of Katy Perry popping out in on the HIMYM gang? And who are some of your favorite guest stars from the show?