What kind of stove do you have? If gas, I would probably steer towards the Member's Mark set since it is tri-ply up the sides. Some say gas flames (or hot elements) can burn your food on the sides of non-tri-ply pots depending on what you are cooking (sauces, for example are vulnerable).

I recently switched from standard electric to an induction stove and found that my tri-ply set did not work since the stainless steel was not magnetic. The Member's Mark set was not magnetic either, so I ended up getting the Kirkland 5-ply disk set. Although I do a lot of sauces, etc., I'm not really concerned about burning since the induction stove does not give off any heat of it's own and the sides of the pots won't likely get hotter than the disk bottoms. If I had a different type of stove, I think I would have opted for Member's Mark.

Both sets look great.

C

I have the Member's Mark triple-ply clad and love it. I did a side-by-side comparison with a friends All-Clad and there was no discernible difference, except of course the price! I actually like the feel of the handles on the Member's Mark better. To me, the All-Clad handles dig into my hands and are quite uncomfortable...they feel as if they've been put on upside-down. Member's Mark is made by Tramontina, who has been making cookware for quite some time. I'm not usually fond of purchasing sets of cookware or anything else, but for the price it cannot be beat. I use some pieces more than others (the large saute pan with helper's handle is my favorite), but I have used all the pieces. In addition to the Member's Mark, I have a few non-stick pieces for eggs and fish, two enameled cast iron for braising and slow cooking, a non-stick 'chili pot', a shallow paella pan, a large disk-bottom saute pan, and some copper saute/fry pans.
Because I wasn't familiar with the 21-piece set at Sam's or the construction (mine is the 11-piece, purchased last year), I looked on Sam's website at the cookware you are referring to. It's triple-ply clad, and for the money it's an excellent deal. IMO, I would buy the Member's Mark and then supplement with a few disk-bottom pans.
I have gas range, and am in the process of looking to 'upgrade' to a pro-style range with higher BTUs. For me, the all-clad type is the way to go, because as cike mentioned, there is a chance of food burning on the upper sides of the pan.
Good luck with your choice.

I got the kirkland set not too long ago and have been using it for about two months.

My stovetop is a Wolf gas one.

I love the kirkland. I am not easy on pots and pans and have a life that is slammin' and bammin' most of the time and my kids do the dishes and don't baby the cookware either.

The kirkland is wonderful

I also use le crueset, revereware, and a brand called.. wait.. I have to go to the kitchen and look at what it says on the bottom..

It says "progressive" and international stainless or something like that.

And, I have some frying pans that are teflon coated too.

I do have two All Clad pans, a saute pan, (like a straight sided frying pan with a lid) and a 2 and a half quart sauce pan. I like the Kirkland saute pan better and I have only used the sauce pan when my brother and his wife visit as she gave me the pan for Christmas about 6 years ago.

I am not a cookware snob, I just like what works for me and my home and what I have - does.

I had been limping along with 35 year old stuff--slowly adding "good" pieces and intending to make a big push for new once we redo our kitchen in Jan 07. DH is our Costco shopper and he brought home the Kirkland set this winter. I'll admit I was dismayed (but wisely bit my tongue). I now am very, very pleased with the performance of this set even on our horrible electric smoothtop range. The pans do rock n' roll on this range but we'll be switching to gas which we've always had in the past. Even my old Revereware does the shimmy. I recommend this set....conducts the heat evenly and cleans up beautifully. It compares favorably with my Calphalon pieces.

I've had the kirkland cookware for 2 years now and I love it, I did a lot of research before I bought it, and as far as I"m concerned it is just as good as the top of the line cookware that is hundreds if dollars more, it clean up like a dream, when I"m finished using it I clean it up with bar keepers friend, and it looks new again.