The Android community has been buzzing about Glide for the past few weeks (new to a lot of people, though it's actually been around for almost a year, since Google I/O 2014). I tried it last July and didn't see much difference from Picasso, so I stuck with Picasso across my projects.
What changed my mind was a benchmark post on The Cheese Factory showing Glide meaningfully faster and lighter on memory than Picasso.

Performance is one thing, usability is another. I don't like fighting a library to use it: if it's hard to implement, it's not really doing its job. Good news: if you already know Picasso, you're in familiar territory. Both are simple one-liners.
// Picasso
dependencies {
compile 'com.squareup.picasso:picasso:2.5.1'
}
Picasso.with(context)
.load("https://lovellfelix.com/images/logo.png")
.into(imgView);
// Glide
dependencies {
compile 'com.github.bumptech.glide:glide:3.5.2'
compile 'com.android.support:support-v4:22.0.0'
}
Glide.with(context)
.load("https://lovellfelix.com/images/logo.png")
.into(imgView);
They're nearly identical to use, but Glide is a bit more flexible (that's a topic for another post). Based on the performance gain, switching was worth it.