In theory any defense or offense could work well under the right circumstances. However, as a coach either here or IRL, you have to constantly be evolving and finding what works versus the emerging trends. Do you play a team that runs 100% of the time? Then a 5-2 would be perfect. Do you play against a team that passes 100% of the time? Then a Nickel/Dime D would be good. Most coaches are going to find themselves in a situation where this isn't the case though and will have to figure out something that will work against the majority of offenses/defense he will face in a season. Right now the 3-4 is all the rage, so find something that you think will work well against that and practice it till you know it forwards and backwards. However, be prepared for that one team that bucks the trend and plays a 4-3 in a world of 3-4 defenses or plays a wishbone in an era of spread offenses. These are the scenarios that give coaches fits IRL. Find what works for you and your situation and build your team around that.