I've got one of each and I'd say that if you've got a worktop to put it on so that you can get a glass under the tap, then I prefer the bottom tap ones. They need less CO2 pressure so the beer comes out less fizzy and near the end of the keg you can just open the top to get the last few pints out.
They might be more prone to leaking, but I've never had this problem.
Also, I use my bottom tap keg as my priming and bottling vessel.
I thought that king kegs only did wide neck versions, but I agree: don't buy a narrow necked version.
Tim