US Stamp Expertizing

Does anyone have opinions on expertizing services for U.S. stamps? I wonder if Weiss Expertizing is comparable to PSAG,PSE,PF,and APS - no relation, but I thought I might send some stamps to them. Thanks in advance - Ken

Art made a poll on this topic a few weeks ago, here is the link
don

https://goscf.com/t/36317

PF is top Hat. APS is also good.

Ken - I would not hesitate to use Bill Weiss for expertizing - outstanding in every respect.

Thank you to all for the info. I'm really having questions of colors on early issues.- maybe it's old timer problem but my #28 looks like all the colors - red brown, bright red brown, Indian red, and the difference in value is substantial. I need an expert to tell me which one. I really appreciate all the advice. I'll try out Bill Weiss, and if that works out maybe he can sort out my #18, 19, and 20 types. These have been collected over many years, and were never certified. Thanks, again...Ken