I'm voting for Lady Gaga (unsurprisingly), and here's why:
1) They're both VERY similar.
Both are rambunctious zany women from New York who love pop culture, know how to command attention, and tend to go rogue in times where it may seem counter-productive to do so. Because of that, my vote for Gaga is my stock in the belief that she is fully capable (and willing) to go as far as Madonna did, hit as hard as she did, and influence pop culture on the level that she did. She may not do it in the same way, since times have changed, but given her track record so far, and her THIRST for ruling the world, I don't doubt that Gaga has a huuuuge career ahead of her.
2) Lady Gaga isn't an asshole.
The impression we get of these women in the public space doesn't paint the whole picture of who they are behind closed doors, but it does offer an inference. Madonna strikes me as a mean girl, and Lady Gaga doesn't. While both are passionate and determined women, and quite brash, I believe that their hearts and minds are in slightly different places. While Madonna comes off as harshly calculated, Lady Gaga comes off as spontaneously passionate. I don't doubt Madonna's passion or Lady Gaga's business savvy, but I don't think Lady Gaga has a "let's fuck them up" mentality quite like Madonna has. And that makes Gaga more interesting to me. Plus, Madonna's been known to be a prick.
3) The talent.
While hardly a hard-hitting vocalist and hardly the greatest song-writer, Lady Gaga's combined talents and showmanship put her up and beyond Madonna's talent abilities. While Madonna is a song-writer herself, it seems her level of involvement in the process wavers depending on the project, and while she's gotten minutely better in the studio, she still can't compete with Gaga's pipes. Madonna's a better dancer for sure, but even with that, Lady takes the cake overall.
4) Lady Gaga is a 24/7 show.
I don't think there's been anyone in recent memory more committed to their job title on and off the clock. Lady Gaga is always on, always dressed for a snapshot, always selling herself or her products, and is constantly ready to talk about something she's inspired by that day. In the social media age where the lens follows you 24/7, that's an incredible feat. Had our culture been this way in Madonna's time, I doubt she would be as committed. As someone for whom her commitment is directed toward, consider me flattered.
5) The promise.
The Madonna career biography, while long and inspiring and amazingly iconic, can now essentially be written in full. We know Gaga has her passion, her gall, her performance abilities, and has already shown a high level of influence in her own social landscape. We still don't know how Lady Gaga will steer the rest of her career, and given how she's said time and time again that she plans to stick around for 30 more years, is there a possibility that she can steer the ship farther than Madge did? She has a couple of one-ups on her side: she doesn't try to rustle feathers (which is handy in the likability department), and she's able to study Madonna's own trajectory and foresee the storms. Madonna is a once-in-a-lifetime entertainer, and her influence can't be understated. But I believe in Lady Gaga. And given her identical footprint to the Material Girl, I suggest you do too.
Now let me listen to the Immaculate Collection today to commemorate the queen, right after I #voteforLadyGaga.