The only problem with YT Editor is you can't add voice overs, which doesn't make much sense. I like Adobe Premiere. Works great on your phone, tablet or pc. It's free for mobile devices, but can be pricey for your pc depending on which version you buy. I've tried all of the main ones that are free and they all have their problems. From my experience you're going to have to spend some money if you want something reliable that consistently works well. That being said, you're using a Mac, which I'm also looking to pick up eventually for my video editing, so I'm looking forward to hearing your thoughts once you find one that works for you.
I've heard great things regarding Final Cut Pro as well, but that price...
S5 tap'n