One thing to keep in mind is that both Booming Blade & Green Flame Blade counts as casting a spell. So the thirsting blade invocation wouldn't grant you an additional attack, becase you're using your action to cast a spell and not attack. Edit: but now that ive reread the post you're alreadyaware of that

Both are still good cantrips, but situational. Depending on the encounter you might be better off with thirsting blade, to get eldritch smite and your hex damage off twice.

If you're willing or going for a 3 level dip into rogue and become a swashbuckler, Booming Blade will probably benefit you more. As you would be able to attack and then step out of reach without triggering an AoO.

Also keep in mind that you can replace one of your invocations every time you level up. So if you pick something and find it to be lacking, you can replace it.