I fitted Cooper Discoverer ATRs on my D2 when I bought it and they were great tyres. Never got stuck in snow/ice (if you're driving sensibly of course), handles grassy fields and light mud surprisingly well, great on tarmac (very good in the wet), quiet, and economical and they were wearing very well. They couldn't handle gloppy or clay type mud though, as you'd expect. In summary, great value and recommended if you're no doing serious offroad stuff. Only 2 ply sidewalls too, so avoid rocky climbs.
I swapped them for BFT ATs. Noticably more tyre roar but not too intrusive, noticably thirstier (I reckon about 2mpg worse), noticably heavier (you wouldn't want these on your roofrack!) however, they haven't worn at all over 15k miles, and they've handled all sorts of terrain with ease. Its safe to say that if my D2 gets stuck now, its down to me not the tyres. Its what the professionals use when overlanding and I can see why. Yes they're expensive, but they deserve their reputation - if you can afford them, then go for it.
I'm fitting Pirelli Scorpion STs to my D1 shortly - they're a road bias tyre and are quiet, economical, great on tarmac and supposedly pretty good on grass and light mud too. A direct competitor to the ATRs I guess. However, my plan is to use these as the daily tyres, and fit a set of mods with more aggressive tyres for offroading. That way you get the best of both worlds - an option for you too perhaps?
BTW As you'll have seen, 16" tyres are much cheaper than 18s and there is more choice. You'll find the ride less harsh on 16s too, so unless you particularly want to keep the 18s, I'd recommend you go to 16s this time.
HTH
