In reply to Jackob:
Both are excellent, but in some ways quite different. Consider the below the generalization - there are clear exceptions!
First, RE grades - British V ice (take point five as an example) could typically equate to WI3-WI4+ (I would say in typical conditions probably WI3+/WI4), depending on conditions and how travelled the route is.
Cogne is definitely more accessible, both in terms of getting there from an airport and necessity to travel once there. It's essentially based around two valleys, so if you're based at the head of either you needn't drive very much, if at all. Getting there from either Turin or Milan (cheap flights from Manchester for you) is very easy (with cheap car hire, even for people <25). The climbing is great, but doesn't feel anything like as 'wild' as some of the Ecrins stuff. Cogne will be busier. But, if on a first trip, you might like the slightly more convenient nature of it. It will also feel safer - more belays will be bolted.
The Ecrins is much harder to get to. Best bet is to fly to Turin, but its then a couple of hours drive over a col (potential issues if severe weather) and then to wherever you end up staying. It's also perhaps not as obvious where to base yourselves - Argentiere? Somewhere in the Queyras? Briancon? I'd recommend Argentiere, but be prepared to head to the Queyras, particularly for your first trip. Will be able to find reasonably cheap accommodation outside of ski holidays and food is cheaper. The climbing is significantly more disparate, but every bit as good. You'll find great stuff from Les Orres to the Pre de Madame Carle to the Queyras to the Fournel and Fressiniere. Some of the stuff in the latter two valleys is sublime, but will take more effort and will feel remote, especially if the roads aren't open! A car is a must and you'll end up using it everyday. Walkins will be longer for a lot of things than in Cogne.
The above is written without considering Ceillac - the playground in the Queyras. Its great, accessible, tame, but busy. It breaks the generalizations of the Ecrins set out above - very short walkins, not at all remote, nice simple descents, tame climbing, will be hooked, etc. But, a great first day venue - get yourself in the swing of things, do lots of pitches (easy to do two or three routes in a day here if you want to, giving potential for 700m+ climbing!).
Ultimately, I think that a trip to the Ecrins has potential to be more rewarding but will require more effort to make it so. It probably isn't quite as good a bet for a first trip, though. It'll be a more reassuring environment to learn to (e.g.) make abseil descents on v-threads quickly, going from one to the next efficiently, in Cogne than the Ecrins.
No route recommendations here as you've not decided on area - if you want any let us know! not very experienced in Cogne, but spent a lot of time in the Ecrins.
Summary: go to Cogne this time, then head to the Ecrins for your second, third, ..., nth trips.
Edit: for both, Ice-fall website gives good conditions updates and camptocamp good topos; for Cogne, iceclimbingcogne is good too.
Post edited at 08:21