I was considering picking up Great Battles Collector's Edition, then I came across the game
Field of Glory, which is newer and seems possibly more robust.

I was wondering if anyone here has played both and can recommend one or the other.

Field of Glory however is quite highly priced, whereas Great Battles is better priced.

http://www.slitherine.com/games/fog_pc

FOG's single-player AI just isn't very good. The battle results can also be rather unpredictable at times. On the plus side, it has a PBEM host built into the game so multi-player is easy. They were supposedly making a big update to it, but I'm not familiar with how that is moving along. I don't really play FOG much anymore.

Great Battles CE is a classic, and one that I still regularly play after all these years. Despite the occasional crash I get with this version. The game mechanics and outcomes make sense and I find the strategy more enjoyable overall.

They're both based on tabletop games. FOG on a miniatures system, and Great Battles on a Hex & Counter one.