For single Player campaigns I am using IL2 DBW (with 24 bit Skins and JTMS sound mod), IL2 BAT, CLOD, BOS and BOM together.
DBW: best for big air battles with many planes, great variety of planes, maps and campaigns
BAT: improved graphics compared with DBW, great variety of planes, maps and campaigns
CLOD: limited planes / maps, I like the Team Fusion single Player dynamic campaign, nice graphics / flight model, runs very well on my Computer, AI sometimes very stupid
BOS/BOM: very expensive, good graphics, nice maps but few planes / maps
For a long wartime career I am starting a il2dcg career in DBW or BAT, after completing Polen39 and France40 il2dcg campaigns I will fly some Battle of Britain missions with CLOD and add the results to DBW or BAT by flying some dummy missions (with unarmed straight flying enemy planes). In the same way I add the results of my BOS / BOM campaigns to my career.