I believe that if you are going to be a true bomber whore you should have a mix of both types of bombers. For most people it is usually personal preference as to which you choose along with which nation you are using. I haven't had a full BW US CV yet but I believe you can choose whichever one you think is more fun or better to use. However, you should probably still have both. ( I usually have 8 main pilots. 1~2 fighters, 3~4 DBs, and 3~4 TBs. ) I think that I am going to start using 24 pilots for each nation though. 8 Fighters, 8 DBs, and 8 TBs. This way I can choose full FW, full BW or mix...
EDIT: As stated above the TBs may earn less experience but they are still fun to use and they still level up, just at a slightly slower rate than DBs. I still think it would be wise to have both types of bombers though.