SourceTree is really nice overall. To name a few things, I prefer its view of history, its hunk selection UI, and its commit message box (GitHub's is tiny and can't be made much bigger). It's also nice that it supports Mercurial.
I had some problems with it keeping changes synced with the file system, though (on Mac OS). E.g., I'd change something in my editor and SourceTree wouldn't pick it up until I reopened the repository in SourceTree.
I also prefer a single window like GitHub's app, but that is a minor annoyance. The non-syncing made SourceTree unusable after a while, and I went back to GitHub for Mac.
I wish Atlassian would put out an update, because I'd prefer to switch back.
Every week or 3 when I restart my machine and reopen SourceTree, it tells me that there's an update. Maybe the issue that you're talking about hasn't been logged or they're not working on it.
I'll try GH Desktop, but for the past few months mine's been broken where it loses my repos, so I've been using ST exclusively :)
Are you on Windows? I'm pretty sure the Mac version hasn't been updated in quite some time. I just downloaded a fresh copy, and it's the same version I downloaded a while back: 2.0.5.2.
Having used both on a Mac (where I mostly end up using the CLI anyway), I'd say that SourceTree is what you want to use for stuff like code review, whereas GitHub (other than local merges being hard to figure out - see my other comment) is quite neat and uncluttered - perfect for small projects or if your workflow revolves around their public repos.
(I don't see why this is being modded down - is it because I failed to mention I'm also using it in Windows?)
I use SourceTree full-time but am keeping an eye on GitUp[1]. The UI is not quite there yet IMO, but it's insanely fast and I love the focus on keyboard shortcuts.
You can however add most 'non-dumb' features you need as custom actions so it's only two clicks away. Now they just have to add customizable keyboard shortcuts and I'd be all raving about it, but still I use it everyday mainly for the staging area.