Since geaux4tigers didn't think I provided any help, here goes....
No rib should be tough and chewy, unless that's what you really like to eat. Before cooking any style of ribs, ask yourself, "what is the end texture that I'm trying to achieve?" Just because someone online says that they should be this or that texture, it doesn't matter. All that matter is what you and your family or friends enjoy.
My take on Memphis style ribs might not be right or wrong, it's just what I like based on my experiences having them in Memphis.

•You can use either babybacks or St. Louis.
•find ribs with a decent amount of intramuscular fat, or moderate surface fat on them, that'll require minimum trimming. You'll want a little on there, since this is a dry cook.
•use a rub that is a good balance of salt, pepper, and herbs with just a pinch of sweet. I may know of a couple. ??
•setup your smoker to cook around 275. I personally like a higher smoking temp for this style, because I don't want them spending more time than needed in the smoker.
•if I'm not going to wrap, I like to have a spray bottle of just water, set to a fine mist every hour or so. Or add a small water pan in the smoker. Some people mop. I just don't like adding anything sweet to the surface during the cook.
•one key is to start to render fat, then to focus on the texture that you like. When you start to see a little bit of the yellow fat bubble up to the surface of the ribs, start checking for doneness. I check mine by pulling on the bones, up and down. Sorta like playing a xylophone. Does that make sense? To me, that's how I can tell the texture or toughness of the meat in between the bones.
•when done, I'll typically add a lite dusting of rub over the top right off the smoker while they're really hot. Let them rest a little, then slice.

Hopefully this helps