Sword Art Online was one of my "entry" titles. When I first started watching anime, SAO was one of my favorites, I didn't like the second arc but that didn't stop me from putting it in my top 5. But I can't really say that as of now, because my taste changes time to time, and I am doubting my love for the series. I would have to re-watch the series to be certain. I'm planning to watch SAO II, after it's done airing.
I don't have much to say about Log Horizon, it didn't interest me much, I'm about half way through and it's been on-hold for awhile. I will finish it eventually and when I do I don't think I'll be picking up the second season.
If you're just comparing these two than I think Sword Art Online will have the upper hand, imo.