What is your goal in sending your cards in for grading? If solely resale, then based on your sales research ($100 vs $30) then it sounds like PSA is the way to go.
If it is for your own viewing pleasure, you say you like the appearance of SGC holders better, so go that route, assuming you feel it is "worth" it to you to pay $50/card (or whatever they charge) for your card to be in a nice holder.
You could always stay raw until it is time to sell, and let the Auction House deal with the grading (or you can sell raw). Depending on your time table, the grading scene could be entirely different landscape than it is now.
If it is for protection, both similar, but Beckett is thicker but doesn't present as well as PSA/SGC.
If it is for online registry, I think PSA is the only one that has it at the moment and is likely responsible for higher resale value.
If you feel the value is in quality of opinion and grade, I feel they are pretty similar in general. Both have stories of under-grading, over-grading, mis-authenticating, etc. Below (sorry for big size) is a PSA 4 in a major auction right now ... guessing it'd receive a 1 if I submitted. You probably don't need toyour card in a holder to know the grade, but hey its your call.
Good luck in your decision!
