As a new tank, I never looked at shield lob as a hate 'stealer'. It's a ranged attack, nothing more.

Correct me if I am wrong, but as GLA, I much prefer to use my gcd on flash. It's the quickest way to grab hate if enmity procs are not available. The way I see things, is the enmity grabber of your combo is best used on that mob that isn't red (if any) on your enmity list, OR the newest mob to enter the fray. If none of these conditions check out, then blast main target with enmity combo.

I dunno if it's a tank thing or not, but you can just 'feel' when you're going to lose hate.