I shop at both. I'm either at Sam's once a week or every two weeks.
I buy mushrooms, English cucumbers (they sell them cheaper at 3 in a pk), pork tenderloins, chicken (if I can't find it on sale at a store around me), rotisserie chicken, cheese, and snacks for lunches once in a while. I also buy spices there occasionally. We also buy garbage bags and kitty litter there when needed. I also use it now to shop for my PTA stuff. My kids are spoiled on their pretzels from the snack shop up front. lol! It just wouldn't be right if they didn't get one to eat before we left.

We are lucky that our Sam's is less than 10 miles away from us now. When I lived in Pa. and in Kernersville, NC it was much further away and I never really took advantage of it.
I do a lot of shopping at Aldi - but if you've read anything about the money incidents where people stole credit and debit card numbers from Aldi members from the south all up the east coast, that stunk. Unfortunately, it happened to me!

Even though my bank ended up refunding our money - I was lucky, I got it all back. Some people did not), the bank froze my debit card and it was a mess to get through. But really, this could happen any where you go.
I like Aldi for eggs, milk, cheese, olive oil, flour, sugar, cereal, juice, some fruit, some frozen foods (they really are improving the quality of some items.). You have to watch the prices of their canned goods now. Sometimes you can find them cheaper on sale at other places. Same with cereal if you find it on sale and you use coupons, too. There are too many items for me to name them all. I'm not crazy about their yogurt, pizza rolls or chopped frozen vegs because they really seem to be bits and pieces.
I don't think that I could choose to shop at one place or the other. If you have the convenience of having both close to you, I would say use both --if you really think that you will use Sam's and not waste the money on a card. Take advantage of their free shopping passes to go and check things out.