Chemistry is subjective, since I see it with Xander/Spike more than Xander/Angel. But talking things in common? Xander/Spike have way more in common than Xander/Angel. Way, way, way, way more in common.Nothing in canon suggests Spike feels anything more than irritation - brotherly irritation at times, but no sexual chemistry whatsoever. Emotionally, Xander and Angel have more in common. He and Angel/Angelus have a ton of onscreen UST.
1) Both losers being picked on by bullies.
2) Incredibly insecure.
3) Don't take rejection well.
4) Both hate and are jealous of Angel.
5) Both had unrequited love for Buffy.
6) Dawn had a crush on both of them.
7) Both don't mind following a woman's lead.
What do Xander and Angel have in common? I honestly can't think of anything except that they both love Buffy.
From that list I have read and enjoyed Xander/Angel and Xander/Giles. I also adore Xander/Graham and Xander/Larry.Potential slash partners for Xander in my head include Angel, Riley & maybe Andrew...if they were trapped on a desert island. I don't like it but I can also see adult Xander w/ Giles. Personally I hate Giles with any scooby. Too incestuous in feeling.
But the best Xander ship out there will always be Xander/Spike. There's a reason why it's incredibly popular.