Best BioWare voice acting?...

This may be too obvious but I do think, Jen Hale has to take the cake here. She delivered extremely high quality constantly over a massive amount of voice lines in multiple BW games, from KotOR to Mass Effect.

But all in all, it's super tough to point at specific people who stand out because most of the time, it's all about interaction and ensambles.

Just individually (and as a matter of personal opinion), I'd also have to mention Ali Hillis because a) when you hear her speak normally, you wouldn't know at all that this is the same person who voices Liara T'Soni and b ) when she does put on "her Liara voice", it is one of the coolest - dare I say sexiest - female voices I know.

But yea, in general, the quality level is so high in these games (even the ones I didn't like that much) that it's hard to pick out specific people.

Claudia Black 

Kristoffer Tabori (HK-47)

I'd say Reyes, Jaal, Sera and Cassandra from the new ones. Really liked their acting.

From older, Meer did ok job and from the ones I remember Miranda's voice was done good even though I never liked ME2 much.
Not really fond of Hale to be honest.

Cassandra, Verric, Isabela, Jane Shepard, Jack, Cullen, Sera, Liara, John Shepard, Garrus Vakarian, Mordin Solis, Grunt, Morrigan and Tali 

I loved her in BSG....so sly and devious and yet sexy as hell at the same time. AND....she's Canadian Eh! In fact, most of the cast on BSG are Canadian (Michael Hogan was born in my home province.... so cool! I had no idea that so many of the cast were Canadian. But back to the topic at hand.....I also really liked a lof ot he voice cast of old games like Wing Cammander and FULL Throttle.....oh yes, and Indira Varma (earlier post above mentioned) as Vivian....she really played up the 'holier than thou", fanciful yet powerful mage role.  Vivian was powerful and she knew it.

well, i really love all the voice acting, so what stands out is the overall level imo.
I dont think i could choose one. Hale obviously lifted a lot and very well, but smaller roles are really good. Meer isnt as good at some points but he did many other good stuff like most vorchas (afair ?)