UB can only be decently countered by 3 Demigods. Oak, Sedna and Lord Erebus. (3 of the 4 toughest DGs... guess who the other is)
Although QoT can use bramble sheild if she even goes close to UB she is screwed
Regulus doesnt have the health or attack to defend himself even if he sits and shoots from afar
The Rook will have his hammer slam stunned and wont be able to run away although he should be able to defeat a UB 1v1 later on if used with tower and healh stacking
TB... You just have to use him right. Avoid using ring of fire as direct offence as you just let him get to you. Apart from that just stay back and bombard with magic
Golgoth has it right in his assessment. UB, Oak, Sedna and Lord Erebus are all slightly better than the other dgs. They aren't impossible to beat with the others, and the others are still viable dgs to choose, but they will never be as good as the 4 I and Golgoth listed. Demigod is definately one of the best balanced games I've ever played, but some dgs are better than others. It's refreshing to see a voice of reason on this board instead of the constant barrage of "stfu the game is balanced", it's not, it's very close, but it isn't.
Also, ON AVERAGE, blood of the fallen is the best item for all dgs except QoT. Yes, in some rare cases assassin dagger or anklet will be better, but at the core hp stacking beats all else...which is why people are so big on sigil.