Here are my favorite type of strings:

The Pirastro Oliv and Olympia strings. Personally I prefer the Pirastro E string and the rest are usually Olympia. One problem I have with my Pirastro E string is that one slight touch of the string and it becomes mute! This is really annoying especially when performing or during exam as I always have to be careful.

I bought the Pirastro string for £14 (ordered online) and the Olypia for £7 at my local music shop :)