a lower lvl 2 hander would be beast for lvling up if you could find one with a long delay. 6.0 or higher. At 90 an sk can do serious work with a two hander..
If the mobs are squishy and your not worried about getting pwned use atwo hander, if the mobs are hitting you hard use sword and board..
and for pvp/BG...
Basically depends on who / what your fighting.. i have a macro for switching between sword and board and a 2Hander.. for instance.. your fighting a mage you would obviously go with the two hander (since block chance dosent even come into play really)
Your fighting a (good) kiting ranger that hits hard you want sword and board + D stance... unless its a totally scrub ranger..