Mitas Co2 are very popular but another option for true on/off road tyres is Pirelli MT21s.
These work better in rocks/gravel/sand or any other hard surface than they do in really slippery mud but they are still OK in those conditions.
To be honest though you will never find a tyre that is fantastic on all surfaces it just isn't possible. You need to make a judgement about where you ride and how often.
If your riding involves a lot of tarmac (whether thats riding distances to get to lanes or commuting to work every day) then go for a trail tyre like the Pirelli mentioned. it will last a hell of a lot longer than a more agressive "off road" type.
On the other hand, if you only ride occasionally, don't do many road miles, trailer your bike everywhere and ride a lot of very slippery, muddy lanes then perhaps a more aggresive competition tyre is a better bet (still road legal though obviously).
Alternatively you could do what I've been doing for a couple of years now and mix and match. I generally run a Bridgestone "GRITTY" ED661 road legal enduro tyre ont he front and a pirelli MT21 trail tyre on the rear. Perfect combo! Great grip and directional stability off tarmac at the front but vastly better wear rate and on tarmac stability at the back.
Weird but it works for me
. i ride a DRZ400E and like to ride to the trails rather than trailer by the way.
Cheers
Richard