I agree Mac is very, very devoted to his job, which is why I think a love interest would be good for him, because both Peyton and Aubrey have shown us Mac outside the lab, 'Mac the man', not 'Mac the detective' which we see all the time. It would be nice to see a different side to him.
Of course, both Aubrey and Peyton are ladies who are very dedicated to their jobs, too, which makes them both a good fit for Mac.
Though if it is Peyton, what, is she going to quit her job in England, and what about her family?
All that said, if they decide to keep Mac single, I won't be too disappointed. But I did really like seeing him with Aubrey and how she brought him out of himself. But if they do decide to keep him single, I hope at least Stella continues to bring him out of himself, show us his more personal side. I like scenes like the one where they go for coffee and talk about Ella in No Good Deed.
I do think that if they do it right, and keep it subtle (not dominate the show) a love interest could be a really good way to develop Mac's character and show us a different side of him.
I'd love to see some flashbacks to his life with Claire, too. If we're talking about 'love interests', well, she's very important, everytime Mac talks about her you can tell he really did love her, despite problems (her wanting kids, him not, Quinn) and that's a very different side to Mac than the 100% dedicated to his job part, although I do think perhaps he became especially dedicated to his job after she died so he wouldn't have to think about/deal with what happened, so she presents both an alternative to and a reason for workaholic Mac, and that's interesting. To me, anyway. We've never really had any serious exploration of Mac and Claire's life together, and I'd love for them to work a bit of that into the show in the future, while keeping the crime aspect strong, of course.
I think basically he deserves a decent, well-written love interest. Grissom had Sarah, and Horatio had Marisol. I'm hoping whoever they pick for Mac, though, they don't do what they do with Horatio's love interests and have them be unattainable (Yelina)/bad news (Julia)/die (that woman he dated who got killed, Marisol), poor Horatio! Mac doesn't deserve that.