Humalog is fine for use in conjunction with GH, or for after-workout recovery of glycogen levels.
For pure mass building, the slow insulins are preferable. I have had excellent results with humulin-N......the all-day time release type insulin. You do not experience the "spikes" common with log or R as long as you eat at regular intervals throughout the day. I gained 11 extra pounds the first time I used N in a 12 week cycle. I was using the same steroid stack and diet that I had used many times before. (also used 10iu humalog with GH after lifting, as always).
I think I did read that serum levels were higher with subcutaneous injections. IM might have been slightly faster, I forget....will have to look for that report.