My biggest issue with Galaxy S2 that I currently own is "device memory" being limited to 2 GB. I don't have any music and rarely take photos, so I end up with lots of free space in "USB storage" (~10 GB) and no free space in "device memory". Getting external SD card helped for a while, but I still have to remove some apps to install new ones and constantly clear app cache and do tricks with *#9900#.
Is situation any better with Nexus 5? I wasn't able to find any information on Nexus 5 "device memory" size and the fact that Nexus 5 doesn't have external SD card slot is worrying.