Why should I choose the 135c over the Avenger Titan for Cargo since it is more expensive?

While the Avenger Titan has a 2 SCU better capability than the 135c and has better weapons, its rework will change where it stands and make it more in line with some other ships around it. The 135c has a very respectable cargo capacity for its size, and its size and fuel capabilities allow it to have better flight maneuverability than the bigger Avenger.