The San Francisco Giants remain the top candidate in the running for Carlos Beltran, if there is indeed a "running." They remain the top candidate simply because it makes the most sense for them to make something happen. They're definitely interested, but as noted, the Mets aren't necessarily eager to get a deal done sooner rather than later. It's a situation they're looking at with extreme scrutiny and if something doesn't get done, they'd be fine with sticking with him.
It'd be a great move for the Giants to make, but it's not like they have a player unhappy with his situation. Those players are generally easier to get hands on. Beltran has made some comments lately, as he reportedly told the Mets that he would be perfectly happy finishing his career on the Mets. He's receptive to anything right now, and has a say in where he ends up, as part of his contract.
"I've already made it clear for the organization that I would love to finish my career here, but at the same time you understand organizations have plans that are sometimes not the plans you think of"
That's a quote from the New York Daily News, and it goes to show that getting Beltran isn't going to be easy. He's happy where he's at, he's a great All-Star player and the Mets would be fine with keeping him on the roster. Who knows what the price is?