How do I choose which version of the IC MT8870 should I use?
The first page of the datasheet explains the suffix codes except for the "-1".


E is 18-pin PDIP
S is 18-pin SOIC
N is 20-pin SSOP
R is tape/reel, for P+P equipment, otherwise it comes in tubes


Obviously if you want through-hole you pick some sort of DIP.

The "-1" suffix is explained under "Applications" as being appropriate for CEPT signaling rather than BT.