The current XPERIA's are not half bad actually. The XPERIA T used by Bond in Skyfall would definitely not be the first choice of a secret agent, but the current Z2 flagship gets a lot of great reviews. By the time it was released to the market it was compared to the HTC One M8, I also saw some opinions saying that these two are currently the best smartphones out there.
Anyway - for sure Bond wouldn't use an iPhone, firstly because Ethan Hunt is using one already (DANG!), secondly and most importantly - iOS is simply too stupid. It's a piece of nice hardware but Android cell phones are far more customizable, which would make it a lot easier for a government agency like MI6 to suit their needs. So I would say that he would go for a solid Android based phone with shatter proof glass. made of steel and maybe waterproof. Something like the HTC M8 or the Z2 makes a perfect choice.
As for Bond 24 it will be probably a flagship, but I think they will drop the Z label by then, otherwise it would be called Z5. I'm just wondering if they will go with a standard version which is pretty huge or the compact one, like the Z1 Compact, which is really nice actually!