I also like tru..good service, but their rates within Europe (except uk) are out of the market... unacceptable high for my standards.
a reliable (personaly tested) and cheap option for roaming within Europe would be Searoam , €0.22/min. for outgoing calls.
http://www.searoam.com/ Also their calls are rated at a minimum duration of 60 seconds and then in units of 30 seconds thereafter. Good customer service and attractive data rates for €0.50/mb within Europe.
*I would skip Geosim, mainly because their service is based on cloud9 network.
Ιf you plan using data as well , ekit Global Premium Service sim (also tested as reliable) has excellent European data rates (except France) for only $0,39/mb (best rate on market) but their voice rates are a bit expensive on this particular sim, which is mainly focused on cheap data roaming.
the price of this sim is also attractive , only $9 per sim. Excellent customer service.
http://www.bunac.ekit.com/ekit/Mobil.../ekglobal_blue