I expected to prefer AACW; I love BOA; I could not get into COG. Yet I prefer FOF over AACW hands down.
FOF is by far the more finished product. This was true, even before FOF was patched and re-patched extensively since it was released last December. But it is especially true now. FOF now plays very historically. AACW is in a teething stage and there are important kinks that need to be worked out. The American Civil War was a huge and long struggle and I do not believe that small developers can adequately playtest detailed simulations of same without the wargamming public's input. AACW will be patched and improved and repatched and reimproved I am sure. But for now, FOF is a more accurate simulation with respect to historical results. (I am relying for the most part on AAR's and forum postings with respect to the historical accuracy of AACW results.)
I did not expect I would, but at least for now, I feel that the FOF system and engine is more appropriate for the conflict. And it is more enjoyable. I find the AACW system unconfortable, at this scale. You make detailed plans, hit the turn button and bam, you get battle results, all without even seeing your units move. This could, and probably will be, improved upon, but for now it is an inferior system to FOF. I understand and appreciate that myriad factors are computed to obtain AACW combat results, but, unless I am able to plan with respect to same, and see my units at least move to the scene of the conflict, I am not able to really appreciate the detail of these factors. The AACW map is exquisite, but I am sometimes at a loss as to where a battle has taken place, the battle results having listed a county without even showing the map. FOF shows you what is happening, shows the armies moving, the site of the battle and, finally, even lets you fight same if you want.
Asked in the abstract, I would probably respond that I would prefer to concentrate on a purely strategic game, without being distracted by detailed battles. But in practice, I simply love the FOF system. It seems to happen every time I play. Just when I am about to call it a day, having had my full of strategy, I am presented with a detailed battle. The detailed battles reflect the strategic situation, are historically acceptable, as far as a simulation is concerned, are a challenge and are great fun.
The non-military (economic, etc.) portions of each game are very different. FOF is much more detailed, AACW much more basic. FOF allows you, via preferences, to hand over much of same to the AI if you like. Both games have significant learning curves.
I look ahead to enjoying AACW as the game improves. AGEOD is a great company and they seem to contantly improve their products, witness the 12 or so patches so far for BOA. I will buy every game they issue (you should also see my Matrix collection.) But for now the bulk of my civil war wargaming time will be spent with FOF.