I have been learning both TacOps4 and BCT Commander and I would say quite simply, they both are very good. I will give you a single pro and con for each that I think sums up these games.
PRO.
1. BCTC. Ability to write scenarios and edit the unit data base. Great for scenario design. If it had a map editor, it would really shine.
2. Fun. Very intuitive interface makes it simple to learn to play. But like chess, not so simple to master!
CON.
1. BCTC. Terrible interface. Screen flashes when scrolling, lots of mouse clicking. Most of the initial learning is how to do something, and this is tedious.
2. No scenario writer for single play. If TacOps had this it would be spectacular.
So, both are good. I would get them both. But if you are interested in a great playing game get TacOps first. If you want to design scenarios and can put up with a clunky interface, get BCT Commander first. (To the best of my knowledge ATF does not have a full scenario editor yet, and this is a drawback..could be wrong here, have not played ATF).