I'm late, but I just have to say that all three of these artists have underwhelmed in one way or another.
Lady Gaga's two songs have had mixed reactions. Born This Way slayed the charts, but it hasn't had AMAZING sales. It's at about 2.3ish MAX million, which is less than S&M, 2.7ish Mill (But, I do understand that S&M had a few months advantage, I'm just pointing out that S&M didn't have the same chart success, but it's still selling more). And Judas obviously isn't performing too well on iTunes either, but it's video is yet to be released, and it could really be a game changer, even though the BTW video really didn't help the song's performance.
Britney, I personally LOVE her album, but it's really not selling as well as it should. HIAM was successful on the charts also, not as big as BTW though, and it had NO longevity, and it's on it's way out of the Hot 100 completely in the next few weeks. TTWE is doing good for a third single, and I think it'll reach a Top 3 peak, and it's been having stable sales.
Beyonce is probably the one that should be judged the least at this point, because her video hasn't even been released, but the song is off to an AWFUL start. Beyonce could easily be called the biggest female act out right now, but her single just isn't reflecting that image. At this point, I don't even think a video would help it out much. So, if she scraps this single, and releases a HUGE hit, then Beyonce could very well be the most successful out of these three this era.

Overall though, I have to say that all three artists have disappointed in one way or another with their "comebacks," but we'll still have to wait for Lady Gaga and Beyonce's albums to come out and the sales to speak for themselves.