Supposedly they are about equal, although in MMBN 3 Serenade tells Megaman (after he's been defeated) that he beat Bass (known to Serenade as "Him" and "He"), although it took him several days to vanquish him. But . . . Bass is stronger. No question. That's why he's the FINAL boss in MMBN 3 and not Serenade. Though it can take longer to defeat Serenade, it is easier.
Free Bass from undernet 7 and delete serenade in 40 secs
Serenade from Megaman Battlenetwork 3 is a boy, as he is referred to by both Lan and Megaman as a boy, and holds the title of UnderKing. I cannot account for other characters named Serenade in the Megaman franchise, though they are likely the same gender.
Nope. He has to share a game with megaman in "Megaman & Bass" for the SNES and GBA.
Find bass after he has fused with gospel
bass hates megaman for stopping him from destroying humanity
Only in Blue, and a reward for successfully completing the Serenade Time Trials. These will be available after you defeat Serenade.
In Megaman Battlenetwork 3 Blue ONLY DarkAura A is available as a reward for completing the Serenade Time Trials. DarkAura is not available in White without cheating. The Time Trials consist of the alpha versions of all previous Navis (excluding Punk, Serenade, and Bass, while Alpha isn't a Navi) which must be defeated in a given time limit with an extra folder. They are available in the Secret Area after defeating BassGS.
No
This, like all "who is better" questions, is subjective. Each character has their own advantages when playable in Megaman and Bass, and they each have cool aspects. However, I personally think that Bass is much "better" than Megaman: his attacks in Megaman and Bass are much more useful against enemy swarms, he is somewhat more versatile, and in general he is just a bad*ss. However, you should draw your own conclusions.
bass
I think it may be in the japanese version only
Square Enix