We adore both and understand they may not be taken well in the US where we live, really struggling since both are special to us, thoughts?
I love [name_m]Klaus[/name_m]. [name_u]Killian[/name_u] just appears quite harsh to the eye, but I do like [name_m]Cillian[/name_m] a little more. I just think [name_m]Klaus[/name_m] is such a sweet name.
Okay so this is a U.K. perspective so may not be 100% relevant but hey ho will try and see if this will help
Ultimately your in a melting pot of a country (similarly to U.K.) in your country unless your living somewhere rural your child will encounter many names from a variety of different cultures therefore I wouldn’t worry. Yes you probably will encounter the odd ‘oh that’s unusual’ which I will admit is hard at first (I get it all the time with my daughter Lilia) but your love most likely will outshine the commentary like it eventually did with me. So I would say go for the name you love they are both strong classics (German & Irish classics of course) and easy to say. I think it could be slightly odd if your not of German/Irish heritage and you choose those names but hey they recognisable and aside from that I don’t think they’ll be that challenging.
I prefer [name_m]Klaus[/name_m]! Such a handsome name. [name_m]Kilian[/name_m] hasn’t ever appealed to me personally but it’s still a lovely choice.
[name_f]My[/name_f] husband is of [name_m]German[/name_m] heritage and I am of Irish/Scottish heritage , so we have been going back and forth between these two classic names 
I do worry about the [name_f]Santa[/name_f] [name_m]Claus[/name_m] thing…
Thank you so much for your response!!!
I love the name [name_u]Killian[/name_u] and actually prefer the K to the C spelling. It’s on my list of potential boy names as well. But I agree that when I hear [name_m]Klaus[/name_m], I think of [name_f]Santa[/name_f].
@hayhay21 glad my response good help ultimately if your husband is of [name_m]German[/name_m] ancestry & you are Scottish/Irish descent then the reason behind your choices are explanatory so I wouldn’t worry about the names not making sense. People question [name_f]Lilia[/name_f] as it’s unusual I explain my mum is Ashkenazi Jewish then it suddenly makes sense. [name_f]My[/name_f] dad is Irish/Scottish as a result I think Killian/Cillian feels very normal to me and I really like it! Yeah [name_f]Santa[/name_f] thing could be a bit awkward good luck with deciding!
[name_u]Killian[/name_u] over [name_m]Klaus[/name_m] but [name_m]Cillian[/name_m] > [name_u]Killian[/name_u]
[name_m]Klaus[/name_m] 
It’s witty and sparky, but at the same time it’s a really sweet and soft name. Probably, he’ll get some Santa’s comments, but it’s not a bad thing after all.
[name_m]Kilian[/name_m] is a darling, handsome name too. But personally, I prefer [name_m]Klaus[/name_m].
[name_m]Klaus[/name_m] is so handsome! Like you said it rhymes with mouse and [name_f]Santa[/name_f] it sounds like claws (where I am) so I don’t think it’d be an issue!
[name_m]Klaus[/name_m] is so handsome!
I much prefer [name_m]Kilian[/name_m] personally, especially spelt [name_m]Cillian[/name_m].
I like them both- I veer towards [name_m]Kilian[/name_m] (two lls) because I like the flow better and tend to prefer Irish names
I adore both of these! [name_u]Killian[/name_u] is so strong and elegant. [name_m]Klaus[/name_m] is cool and interesting! I think i slightly prefer [name_u]Killian[/name_u]
I like both, but [name_m]Klaus[/name_m] feels a little dated to me. [name_m]Kilian[/name_m] gets my vote, though I personally prefer the [name_u]Killian[/name_u] spelling.
I love Klaus,Killian reminds be of kill/killing
I love them both and have them on my list.
[name_m]Klaus[/name_m] because it’s a surname in the family and it’s sweet and cheery and I like [name_m]Klaus[/name_m] from Umbrella Academy. I like Klausie as a nn but I don’t like that the name reminds me of clowns.
[name_m]Kilian[/name_m] because I’ve always loved the name and Irish connection and I liked Kili from the Hobbit. [name_u]Lian[/name_u] is a cute nn.
I like [name_u]Killian[/name_u]! Its like the “male version” of [name_f]Jillian[/name_f] and think it’s really cool and unique.
It depends on where in the US you live. I grew up with a [name_m]Claus[/name_m] and he had no problems. [name_m]Kilian[/name_m] won’t be in issue either as I’ve heard of people named [name_m]Kilian[/name_m] here as well. The question is, which one would you regret not using if you only have the chance to use one?
I really like [name_m]Kilian[/name_m], and I like the way you spelled it. I think it would need to be spelled out a lot of the time for people but if that doesn’t bother you, I think it’s a great choice.