Procedurally generated maps would allow for nearly unlimited map layouts causing your game to have a ton of variety, however it would weigh in on your time to program as much. An alternate option is to create a set of pre-designed maps and randomly select one of those at game start to keep the game from playing the same almost every time.

I think it would be a good idea to have at least more than 1 predefined map layout in the game though. It would prevent the game from falling into the trap of having a "solve the puzzle" type of game play. It also would mix it up so your players aren't always trying the same stratgey so it has more replay value.

Predefined maps by nature do sort of fix your variables for balancing and benefits in strategy games generally, but with even a little bit of variety this can at least be diluted a bit.