If raw strength in the power is considered, then Aginor is second to Ishamael. But as you've pointed out, Aginor was a sniveling little weasle with no skill. Without skill, Aginor's superior strength means little which is why that loser grovels before Demandred and many of the rest.

Aginor knows he has less skill as a weaver than the other chosen and he lacks the combat instincts that are crucial (see Demandred's ability to immediately ascertain what he is up against at the end of Winter's Heart compared to the other chosen's reactions) to one power duel. Aginor can channel more of the power than anyone except Ishamael, but Aginor's below average skill and battle prowess make him less of a threat than others like Demandred who might be able to channel slightly less power, but more than make up for it with superior skill and instincts.

It looks to me like you've defined powerful as a mixture of raw one power channeling ability, plus skill/dexterity, plus battle instincts. With that many factors to look at, Robert Jordan hasn't given enough information to make certain conclusions.

But just between you and me, Sidious, I'm the second most powerful!