Worked for both of them - EZY and EZS - for about 18 months each on my 3 year stint.
Pay: Pay started at a franc equivalent of UK pay - stagnated when the UK pay went up and no amount of representations could change that - even though Geneva is (or was) the second most expensive city in Europe.
Food: Food (Gate Gourmet) was magnificent in EZS - the problem was trying to organise your flight to allow time to eat it properly. Quite an improvement on the bacon and beans / sausage and beans / omlette and beans and beans and beans of Alpha.
Flight duty: the Swiss regs applied to EZS - actually allowing 100 block hrs per month. Didn't happen too often. EZS actually came from TEA Swiss originally and had quite a laid back charter mentality - rather than the go-go mentality of EZY. They soon got the hang of it though.
Attitude: There was in GVA a fair bit of distrust of the HQ in LTN - a not undeserved feeling of being the forgotten base - and the language difference didn't help. There were some very good operators there though (in LTN too, it has to be said) and they were a good choice for the A319 intro. This may help cement things on the ops side.
This info is based on conditions just over a year ago.