Here's what I believe, and I'm sure I'll catch a ton of crap, but if you're not mature enough to have an adult conversation about this topic, then please don't respond.
My personal belief is that most snakes are not very keen on human interaction. Most snakes don't really gain anything from human interaction. I work with a lot of snakes through work and in my personal collection. I read body language every day, and it's become almost second nature now, reading a snake or any animal for that matter, when I look at it.
As far as what species are more intelligent and tolerate handling better, Asian Ratsnakes for sure are more intelligent. King Ratsnakes, Radiated Ratsnakes, Beauty Snakes, they all seem to posses a type of intelligence and can identify keepers and will tolerate handling better than say Garter Snakes which are (from my personal experience working with Natricine snakes), much less intelligent. Most of your New World Ratsnakes (Corns, the obsoletus complex, etc), are relatively intelligent, but I don't believe that they actually posses the intelligent that Asian Ratsnakes or Elapid hold. Cornsnakes, are by nature docile animals, and usually tolerate handling extraordinarily well. Personally, I don't handle mine very often because they do just fine without it. It is a matter of opinion, and my personal opinion is over handling can stress a snake out and in general handling is not something they particularly enjoy.
I have noticed that some species like Reticulated Pythons, are very intelligent, but a close relative of theirs the Burmese Python, is not particularly smart. When I say it comes from my observations, I mean behavior study. When I watch a Retic, it will look right back at me a respond, usually by coming in closer, increased tongue flicks, and sometimes lifting it's head about the ground to see what I'm doing. Retics also learn to identify their keepers which I have never seen but I know many people who this has happened to. With Burms, it's a different story, they are concerned about food and when I open a Burm cage they want to eat me 99% of the time. They don't make eye contact or seem very interested in me being around unless I'm feeding it.
Snakes in general are not particularly intelligent individuals, they do have the capacity for some primitive learning, but they're not going to come to you for handling. As far as emotions, I don't think they necessarily posses a ton of emotion. I don't believe they can feel something like loss, or elation. Snakes are very hard to read even for people that have been doing this for a long time, and because they're faces are so emotionless, it's very hard to get a real feel for what's going on in their heads.