I also felt that Gerber was small. I only used Gerber NB size with DD, but they were perfect for those first couple weeks.
I thought that Carters were pretty spot on with the ht/wt sizes on the tag. Although I will say the Carter's brand sold within Target seemed to be bigger than ones bought at the Carter's store itself.
Each baby is different, some are longer and skinnier, some are shorter and chunkier....so there isn't going to be one universal answer here.
My daughter would go through growth spurts - either up or out - and she would outgrow one of the measurements. Seemed like she would always have clothes on that were too loose/baggy or too long.
Now that she's older, I find some stores more in line with her body type, which is tall and skinny. Gap and Gymboree fit her best. Children's Place tends to be smaller.
My suggestion is to keep everything - you will use it. Some clothes that you think might be big for their size are actually going to be perfect for that 'in-between' phase when you are about to move up a new size entirely.