I don't know if it's the best, but I recently got a Scicon AeroComfort Tri 3.0 for my bike, which happens to be a Trek Speed Concept size L, maxed out on reach. While I still remove the extensions just to be safe, they easily fit in the case. It's a softcase, yes, but padded and armoured in all the right places in my opinion. Packing it is a breeze.
I'm certainly very drawn to this case for the ease of packing, but im worried about what happens if it's mishandled, or something gets dropped on top of it. I think I'd probably be too anxious about the possibility of damage
Although the shipping is very expensive(about $250), the bike box alan triathlon easyfit is looking like the best option. I'd rather pay a bit more for a hard case that doesn't require disassembly of the front end of the bike.