I tried the Ultralight C the other day on a friends device, and it wasn't working. I raise these concerns because I know the Mifare Classic tags don't work with Blackberry, and I was trying to find a tag that works on majority of devices.
I still haven't tried the Ultralight Tags.
Any information anyone has on this issue would be helpful.
Nexus 7 contains the same NFC chip (PN544 by NXP Semiconductors) as Nexus S, Galaxy Nexus, Nexus Q, Samsung Galaxy S3, HTC One X and many other Android devices. So all these devices support the tag types in principle (antenna performance may differ, leading to somewhat varying results). Blackberry contains an NFC chip by a different manufacturer. MIFARE Classic is a technology by NXP, so it is supported by NXP's NFC chips, but generally not by other manufacturers.
When choosing a tag type that should work on all (or the majority) of devices, I would choose one that implements one of the standardized tag types by the NFC Forum:
I have tested all these types both with Android devices and with Blackberry and they all work. The main difference between the various types is how much data they can store and how easy the data can be protected from overwriting. Most of the named examples above are generally available from various online vendors.