To correct some misinformation scattered above:
Both arty and infantry bde use 100 officers
Inf use 3.33 manpower while arty uses 1.33
Arty uses 1 supply while inf uses 0.67
Arty and inf have the same speed [unlike HOI2]
If you have enough leaders/officers, then adding arty to infantry is generally cost effective. For your typical combat width of 10, 3 inf + arty with 4 divisions per corps is probably the most effective combination [16 attacking bde]. You can also use 2 inf + 2 arty to create a breakthru corps of 5 divisions [20 attacking bde]. Drawback to fewer inf bde is that they are not so good if they are on the defensive.
If you do not have a lot of leaders/officers, then stick to plain inf. Arty bde use as many officers as inf bde. Best corps set up when you do not have lots of leaders/officers would be a corps of 5 plain [size 4] inf div, rearrange inf bde into the HQ to make them fighting formations, with 6 fighting divisions spread out over 2 provinces.
And to stretch that even further if you do not have enough leaders/officers, substitute militia for infantry on a half and half basis: 12 militia, 11 inf, and an HQ for 6 fighting divisions in a corps spread over 2 provinces.
http://www.paradoxian.org/hoi3wiki/Strategy has 2 articles about division building which might be useful with links to some forum discussions. Lots of discussion about this in August.