My main money league that I commish is a 14 team league and has been for years. I honestly couldn't envision it any other way.
Here's what we do to keep things fresh and competitive:
1. Two divisions
2. You play every team in your division twice and non-division teams once for a total of 19 games. (I guess you could simply play each team exactly once but that really sucks for bye weeks IMO.)
3. This means double game weeks on weeks 3, 5, 7, 9, 11, and 13.
4. The division winners get bye weeks for the first week of playoffs on week 14.
5. Use standard NFL style rules for matchups in week 15 instead of immutable brackets. The top seed should get the advantage.
We also use the following settings:
The reason we go with 2 flex spots and only require 1 RB is because when we did 2 RB spots required it was simply an RB land grab for the first three rounds. All other positions were completely forgotten about and if you had one RB go down you basically could write off that season because you're using an RB that shares time for sure as one of your main RBs. It also allows for people to use two different methods of acquiring a good team, either by fantastic RBs or WRs. Some have even tried a TE route although that was met with little success (we do score TEs differently for yardage though so this did make a *little* sense).
The draft lasts 15 rounds. This amount is good because you *could* draft an entire team that fits the above mold and never need to pick up another player. We don't have any IR spaces. Going an extra round would really sweep up the remaining players that have value and going with only 14 roster spots means you *must* drop a player at some point during the season or play with an empty roster space (something I forbid in my league).
If I think of anything else I'll add it in.