Do you fly SU or OK?

Lounge access is important; however upgrades to business class could be very valueable as well. Note that for these upgrades you will need to fly CSA and an eligible booking class (meaning not the cheap fares).

Basically I would suggest you enter the program of the airline that you will fly. OK+ is nice if you dont fly the cheapest fares, as you get lounge access in PRG with Silver and you can get upgrades to business for free. SU's program I am not very familiar with unfortunately.