I don't use cases anymore, specially with the N5 which is already a really big phone.
Now I am using a Nillkin H+ tempered glass of 0.3mm.
I don't think I am covered from a fall but I'm sure that the risk is mitigated.
There is a lot of people who dropped their N5 with this tempered glass and the only destroyed thing was the Nillkin glass. But i'm not sure which of them have used a case.
Nexus 5 (Stock + Franco Kernel) - Galaxy Nexus (CM11 + A.S.K.P. Kernel) - Nexus 7 2012 (Stock); Galaxy S GT-i9000 (CM11 - zRAM OFF); Galaxy Y Pro B5510L (Stock).
Nexus 4 16GB; Galaxy S3 GT-i9300.