so what are your favorite; of the baddest of the bad in the Marvel ans DC universe…
Norman Osborn (Marvel) and Joker (DC)
Both are classic, simple, and batsh*t crazy
Two Face is probably my favorite villain in any comic. I’m just a sucker for the whole “fallen hero” angle, and I really love the way some writer’s explore his psychosis. It makes for some gut wrenching scenes when Batman has to take his former friend down.
For the Marvel U, I gotta go with Magneto. He’s so brilliant and he’s an incredibly complex character with some twisted, but noble intentions. I think a great villain is one that you can sympathize with on some level and both Two Face and Magneto do that for me.
I would go for Talia for Dc. Bad brilliant girl are sexy. Even Batman would agree 
Marvel is a tough cookie, they have some incredible rogue gallery but I would settle for Loki. My favorite interpretation of the character would be in The Ultimate.
I know, I’m weird
Although I was classically an Avengers guy vs. an X-Men guy, I always felt that the x-men villains stirred deeper feelings in me. The root of this is that in many cases, their brand of evil stems not from a Dr.-Horrible-esq desire to rule the world, but instead from extreme prejudice and ‘racism’ toward the mutants. That always made it more real for me.
The two sides of the coin there are the Sentinels (esp. in one future line where you see one disintegrate wolverine to where there is nothing but an adamantium skeleton), and both Apocalypse and Magneto.
Re: the sentinels, they represented the same kind of evil that both the terminator and zombies represent in their respective genres: unstoppable and uncaring killing machines that can’t be reasoned with. Except that their ‘motivations’ stem from programming related to that whole racism and genocide of the mutants thing.
The inverse is the ultra-mutants rights villains. For me (and I know I’m in the minority here) Magneto suffered from the “yeah, yeah, we’re heard it all before” villain syndrome. While I agree that his deep history has allowed the character to develop and grow, back in X-Factor when Apocalypse took angel and created the horseman of death, we saw a Villain able to corrupt one of Xavier’s first students. If someone that noble could fall, what did it mean for the rest of us.
Sorry for the epic ramble.
TL;DR: the Sentinels and Apocalypse in Marvel. No informed opinion in DC.
Talia’s an inspired choice. Can’t really disagree with that at all.