I was always told that both were equal, but I have come to disagree with that based on my own experience. Until this current boat, I always had iCom, but I became very frustrated with their defective N2K support, so built this boat with SH VHFs.
Right from the start, I was surprised by the difference in reception quality and clarity. Commercial VTS traffic in Puget Sound, for example, used to always be crystal clear with my iCom VHFs, but instead was always scratchy with the SH radios. I checked all the usual stuff which seemed fine, so decided to try the equivalent iCom. No other changes, just moved the antenna connection from one VHF to the other. I have/had two identical VHFs in the boat, so this left me with a SH and an iCom operating side by side.
All I can say is, wow, what a difference. With the iCom it was right back to the clarity that I remembered from my previous boats. I have since replaced the other SH as well.
Now I'll say that I'm still not a real fan of iCom other than with respect to the core radio performance, which I think is clearly superior. But core radio performance is what's most important, so I prioritize that and tolerate the rest. I also agree with the comment about cost. iComs and noticeably more expensive.