Personally I would say PartyPoker now have the best format for satellites especially with the re-introduction of tournament dollars so you are not restricted to a specific target event or a 7day expiry ticket as all T$ won have an 12 month expiry and can be used however you like. For example if you win 109T$ you can play a $109 event or several smaller events offering more flexibility.
They also still have the feeder satellites to their special/flagship tournaments/series such as partypoker million or millions online.
I liked very much the big fish satellites on 888poker , so easy to get one ticket , even not good players like me Unfortunatelly now 888 has left Greece , so sad for this . Also Pokerstars has many satellites especially for big special events/promotions , but I have to say too many good players you have to compete with to earn the entrance there , difficult for me