Hi
Any really mxs 5.0 is most common
I have the genuine jaguar one which is only a 3.3 amp, which does the job perfect
theres no benefit to getting anything bigger, wont charger the battery any better or faster, as its a smart charger and does it in processes, then when complete it turns off and stay in standby sort off, when the battery voltage drops it starts charging and goes through the same process again, this is why these can be left on long term and wont over charge or boil the battery dry, like cheaper ones
you can also get convenience kits that you fit. mine has a small socket in the boot, you just open the boot and plug it in and its maintaining, no need to lift carpet ot get to the battery
also if you fit anything connected to the battery, like one of the sockets or quick connect kits, make sure its a fused type as close to the battery as possible, some kits are not fused, and if you trap the cable by accident, it will just melt all the cables or possibly start a fire.
cheers
Joe