I have both Costco and Sam's club memberships...
From where I live, the nearest Costco is 27 miles away... from where I work, it's one mile away... I pretty much feel that the discounted prices on gas alone pay for my membership at Costco, so regardless of which of the stores is better, I will keep my Costco membership...
Sam's... There is one about 13 miles from my home.. ( in Jackson ). Often on weekends and other times, I'm near there, so regardless of which store is better, I want to keep my Sam's club membership... even though my wife wants me to drop it...
IMHO, Sam's Club is just ever so slightly the lesser of the two membership clubs...
I don't know that they ever carry any PRIME meat, where Costco does. Now, I rarely buy PRIME meat because I don't see the value in it for me personally, at least not very often. The exception being Costco's PRIME brisket... and the main reason I buy that , is it's not really expensive... My Sam's rarely has any kind of Brisket for under $5/lb, and Costco sells the PRIME for $3.29/lb right now. Sam's has reasonably good meat , at reasonably good prices, but Costco has slightly better meat ( non prime ) at the same prices as Sam's. Sam's does sometimes mark down meat as it hits the sell by date, when I'm there , I always look for good deals of this sort, my Costco never seems to have any meat that hit's the expiration date, so never any deals of this sort...
For some odd reason, there are certain things that Costco just doens't sell, but Sam's does sell , bulk bags of pepperoni for example... Price of pepperoni has gone up recently it seems, and I use enough of it that I do buy it in bulk, then vacuum seal it up in smaller bags, I feel better about my pepperoni purchase price doing this. I'm not 100% sure on this, but I don't think Costco sells uncooked bacon either... Not that I buy much bacon these days , since I make my own ( using pork belly from Costco )... On the other hand, my Sam's rarely has pork belly for sale, and when it does, it's like 50% higher priced than Costco...
The main issue with these stores, and what probably should be your deciding factor, is are you really going to buy in bulk... and where will you store the 'bulk' that your not using at the moment? Most of the really good values are related to bulk purchases... Like even toilet papper... you have to buy like 50 rolls at a time. ( I've heard that toilet paper is one of Costco's biggest sellers, I assume Sam's is the same ). Yes, there are good deals to be found on single items of things, but how many times do you need a slow cooker that's $5 cheaper then what you can get at Target?
So, my advice would be go to Sam's , I think they very likely will give you a guest pass for a day. ( not sure if you'll actually be able to buy using it though )... Look around, see what you see, figure out if it's worth your time... And/or just buy a year membership... Not 100% sure, but it may be the case that you can return your membership if you don't like it ( I know Costco will let you cancel your membership for full refund )... But anyway, if you like what you see on your day trip, get the membership ... at worst it's a $50 gamble... If you find you don't use it much thorough the year, just don't renew next year...