I am a mere Plat at present so FL doesn't matter.

Longer flights I don't mind - the extra miles are always welcome, though not required at present.

All three are good by price and schedule. So the criteria would be if certain flights tend to go less overcrowded and the chances of clearing an upgrade. This is in future, so how the flights look today wouldn't help, I would need to extrapolate the historical experience and take my chances.