Sony selling Spider-Man would be MARVELous! I am a huge fan of super hero movies. Although Sony does a pretty good job, I think that Marvel would add better special effects, better actor/actress selection, and a better storyline. Sony gets paid and the public would get a better Spider-Man movie in the near future. It's a win-win situation!
Yes, Sony should sell its Spider-Man rights to Marvel Studios. Marvel has had an insane amount of success with their recent Marvel ventures, including the stories of Thor, Captain American, Iron Man, and the rest of the Avengers. Spider-Man on the other hand has required two incarnations of the character is a decade. Giving Marvel the rights to Spider-Man would allow them to include him in their other character movies, likely giving a popular character more of the good attention that it deserves. The newer Spider-Man movies, starring Andrew Garfield, are much better than the previous Tobey Maguire franchise, but it could be taken even further if handed over to Marvel.
No, Sony Pictures should not sell its rights to Spider-Man to Marvel Studios. Spider-Man is one of the most well known and important superhero of the last 50 years and Sony Pictures is lucky to have it. They shouldn't give up the rights unless they financially are forced to. I understand that the last couple movies haven't done as well as they'd like but the loss of money from losing the film rights would be even greater. It would be smarter for them to take a break from the franchise and come at it again in the future with new ideas.
There is no logical reason that Sony should sell the rights to Spider Man to Marvel Studios. The Spider Man franchise is among on the most valuable revenue streams that Sony Pictures has. Spider Man films and product licensing produce hundreds of millions of dollars No reason it should be sold.