I use Durham. Currently in year 2012, and in division one for County and National League.
But it is your choice. Might wanna use someone easy, like Hampshire.
FoOr bowling, set the bar on full (V.Aggressive) at all times in FC games, and in OD games leave it one 3 at all times. Let your two opening bowlers have attacking fields (Second most attacking in FC, 3rd most for OD), then when you make a change loosen the field a bit. That's it really. And bowl to their weaknesses, and if the batsman doesn't have a preferred line, bowl on guy on leg and the other on off. Also, they both MUST be bowling to different lengths.
Thats it.