Springer all the way, mate, especially if it's going to be your main gun
Co2 does have it's uses (I use it...) but as an all year round hunting tool it's limitations far out weigh it's advantages of being small, light, compact and very quiet with a mod fitted but the ballache that goes with it, cost of Co2 soon mounts up, general shitty quality of most of the guns, no use at all when it gets cold, unpredictable shot count etc...
As has been said above, get a decent used springer, any HW, Air Arms, Diana or older UK built Webley (don't buy a Lightning, they're shite!! ) will do you ju