Much of the leather offered in the US these days is imported, usually from Latin American countries, and tanning methods vary considerably (in some countries it is fairly common practice to use animal feces and urine in the tanning process).
I recommend vegetable tanned cowhide from either Wickett & Craig or Hermann Oak tanneries. But both of those sources require more substantial orders than a hobbyist can justify (6 or more sides, roughly 150 square feet). For smaller quantities I suggest that you contact Springfield Leather (very nice interactive website, should be easy to find). Springfield stocks Hermann Oak veg-tanned and will sell by the square foot. You will pay a little more with shipping expense, but you will have more assurance of getting quality leather.
As rednichols mentioned, you should avoid leather with loose or stringy flesh sides (inside of the hide). Also avoid leather cut from the bellies, which is quite variable in both thickness and strength and seldom makes a decent holster. Shoulders usually work well, and backs are usually very good.
You asked about advantages of holster lining. Lining (either suede or smooth leather) has long been a popular method for protecting the handgun finish from excessive "holster wear", which is abrasion caused by holstering and drawing, as well as movement of the handgun inside the holster during carry. A 7-8 oz. leather holster body lined with a 2-4 oz. soft leather makes a very serviceable rig.