I love the name Hayden. I used it as my user name for years haha. I love it on a boy as well, though. I've been crushing on Dean lately as well. The D's clash a little in the combination of Hayden Dean, but the styles fit nicely.
I like Andrew well enough, classic and handsome. Two equally handsome and classic nick name options as well, if wanted. Cliff is alright. Not my style, but flows fine with Andrew.
Kellin isn't my style, sorry. I don't tend to love any "kel" names though. I don't care for James either, though that's due to personal associations.
For whatever reason, I've never cared for Seth as a name. It's alright, just never been my style. Ambrose is alright.
Funny enough, my partners brother is Nicholas Adam. I think Adam Nicholas flows nicely, I like Nicholas. Adam, however, just isn't my style.
I like the name Austin. It's not one I'd use IRL but I like it. Both Austin Michael and Austin Nathaniel flow nicely. For this one, I'd base it off the surname as to which goes best haha. Both go really nicely! I think I prefer Austin Michael in general, though.
Derek is alright, I knew a lot of Derek's growing up. Many were in my classes.. so it feels dated to me. Like it should be on a guy in his late teens/ in his twenties. Allen/ Allan is alright. I prefer the spelling "Allen".