I'll say default WoW ui is the best....

U can always try using nurfed or CT_Bars for bar mod..

here's a tip...use as few bars as possible..here's a way to organize ur buttons without having too much icons on ur screen

Set 1(shift 1) - abilities that u use when solo
Set 2(shift 2) - abilties that u use when in group/instance/raid
set 3(shift 3) - ability that u use in pvp/bg
set 4 (shift4) - others .