At the time that Angel and Buffy slept together (Season 2) she was 16. If we consider Angel to be suspended at his human age, that would make him the equivalent of 25-30 years old, or almost twice her age. For a high school sophomore, that's pushing it a little.
In Season 6, when Buffy and Spike first tore the house down, she was about 20, a young adult by anyone's standards, and Spike was the equivalent of a 25 year old man (I believe either Marsters or Whedon mentioned that age somewhere, or maybe I'm just imagining it).
Comparing the two, Spike/Buffy seems a bit more "proper" to me.
If it's of any interest, the age of consent in Georgia is 18, so, at least here, Angel was the one who bedded the jail bait.
Just wanted to point out, the episode "Surprise" actually occurred on Buffy's 17th Birthday, so she was 17. And if I recall, Angel was about 25 or 26 when he was sired, so that's a max of 9 nine years APPEARANCE difference. Keep in mind, at this point Angel is around 250 years old, in reality.
Which leaves him with very few dating options in his own age group
😉
And even if he dated a 26 year old Buffy, she still hasn't been around nearly as long as he is, and a 225ish year difference is a lot. And yes, I know, he looks like a 25 year old but that's the whole point of vampires: they always look the same age, no matter how old they actually are. I'm not saying he should go after 12 year old girls on those grounds (there is a level of common sense, and laws, to go by), but I think Buffy was more than old enough to make her own decisions about her sex life (otherwise I'm sure the writers wouldn't have allowed it).
And in Canada, the system is a bit confusing, but this situation (a 17 year old and someone older, with consent) as far as I know is legal, so he couldn't wind up jail bait here in the good 'ole Canada (although maybe if anyone could find the ones from 1997 CAL, that would be the most revelant
😉).
It really is all in person opinion though, I myself find it acceptable, under the circumstances, but if someone doesn't think so I can understand that too.