Is it [name_f]Caitlin[/name_f]? Or it could be [name_f]Katelynn[/name_f]. Whichever spelling is truly the most normal, I’m sure we’ll have some different opinions here!
ETA: I’ve seen [name_f]Kaitlyn[/name_f] the most often, but I honestly prefer [name_f]Katherine[/name_f]/Catharine nn [name_f]Kate[/name_f]/Cate!
Caitlin, imo.
I think [name_f]Caitlin[/name_f]
My favourite spelling is [name_f]Caitlin[/name_f], but I’ve also met people who spell it [name_f]Caitlyn[/name_f], [name_f]Kaitlyn[/name_f] and [name_f]Kaitlin[/name_f]. I’ve never met a [name_f]Katelyn[/name_f], but I know that that’s quite common in the US too. If I met one, I’d probably just ask.
I’m inclined to say [name_f]Caitlin[/name_f] as well.
Kaitlyn. I don’t think this has been mentioned, but I saw it and this was what I first thought of
Kaitlyn is the standard where I live, followed by [name_f]Katelyn[/name_f]
This one of the few names where I really don’t think there’s a “standard” spelling. I know [name_f]Caitlin[/name_f] is the original, but whenever I meet a “kayt-lin” I immediately ask for the spelling.
I agree with [name_f]Caitlin[/name_f]. Though I’ve only ever met [name_f]Kaitlyn[/name_f]’s, nn [name_f]Kate[/name_f] or [name_f]Katie[/name_f].
Caitlin 
Definitely [name_f]Caitlin[/name_f].
It’s [name_f]Caitlin[/name_f], and I like it much better than any of the other spellings. But I still prefer [name_f]Katherine[/name_f]/Catherine.
I agree that there are so many variations I’m not sure if there’s a “normal” spelling these days or it could be regional. You could check past popularity charts to see which spelling is most common. I’ve seen [name_f]Caitlin[/name_f], [name_f]Katelyn[/name_f] or [name_f]Kaitlyn[/name_f] the most.
Caitlin, but I agree with preference for [name_f]Catherine[/name_f].
I like [name_f]Caitlin[/name_f] or [name_f]Katelyn[/name_f].
[name_f]Caitlin[/name_f] would be my first thought!
In 2019 in the US…
[name_f]Kaitlyn[/name_f] #444
[name_f]Katelyn[/name_f] #532
[name_f]Caitlyn[/name_f] outside the top 1000, #599 in 2015
[name_f]Caitlin[/name_f] outside the top 1000, #609 in 2015
[name_f]Kaitlin[/name_f] outside the top 1000, #837 in 2012
My preference is definitely for the K spellings.
Caitlin is probably what I’ve seen the most, but I much prefer [name_f]Kaitlyn[/name_f] or [name_f]Katelyn[/name_f] (this is how my cousin’s name is spelt)
Katelyn is what I’ve seen the most. Rarely come across the C spellings.
I think the classic spelling is [name_f]Caitlin[/name_f], however in the US we like to spell thing so phonetically so I think [name_f]Katelyn[/name_f]