The Spartan 3/3E/6 lines are legacy parts (and hence stuck on ISE for programming, so you don't want them). The Spartan 7 parts were a late addition (not shipping until 2017) to the 7th gen line for the low end; they use the 7th gen blocks and tooling, but are "cost optimized" and lack the fancy transceivers and such - though irritatingly the cost and resources of the Artix and Spartan parts have a lot of overlap; Spartan7 parts run from about $15-140 in single, Artix7 parts from about $25-430.
The Spartan 3/3E/6 lines are legacy parts (and hence stuck on ISE for programming, so you don't want them). The Spartan 7 parts were a late addition (not shipping until 2017) to the 7th gen line for the low end; they use the 7th gen blocks and tooling, but are "cost optimized" and lack the fancy transceivers and such - though irritatingly the cost and resources of the Artix and Spartan parts have a lot of overlap; Spartan7 parts run from about $15-140 in single, Artix7 parts from about $25-430.