When you buy a reference set look for 1) quoted by the people you buy coins from 2) has a lot of coins of the cities you are interested in 3)
good photos of
good coins.
The two SNG sets I see most often and plan to buy are
SNG Copenhagen and
SNG von Aulock. Copenhagen is far more
complete (22,012 coins) and coverage of the entire Greek world. It is also in English.
Von Aulock has 8739 coins and is in
German. It only covers
Asia Minor. Unlike Copenhagen, the VA coins were sold at
auction and
still show up occasionally for sale.
Unfortunately I haven't found it possible to buy these on the installment plan. I've instead been
buying SNG ANS and SNG British Museum as volumes come out.
If you mean individual volumes, I would love to get
SNG Levante. It is a single volume SNG (plus supplement). I've never seen it for sale, though. It only covers
Cilicia.
SNG volumes don't have any text other than basic descriptions of the coins pictured. Lately I have been spending my
money on books with more written substance.