OP, none of us can really make the decision for you. What I will say is that I think the Nexus 4 seems fantastic value, but like you say the spec is very similar between the two phones - so personally I'd say it comes down to if you want a Nexus phone with all the Google updates on time, as there's not much in it hardware wise. Of course there are plenty of AOSP-based ROMs for the GSIII which will probably hit not long after the official Google updates, if you want to run "pure Android".
I'm really tempted myself by the Nexus 4 (currently running a Sensation). I've realised that with every phone I own I end up picking the ROM that makes it as close to AOSP as possible, so I might as well get a Nexus where that's your starting point. Plus, the Nexus 4 has the fastest hardware out there (maybe the Exynos scores 10 points more in some benchmark but for all intents and purposes I see the Exynos Quad, S4 Pro and Tegra 3 as more or less equal), quite possibly the best screen out there and what I think is a pretty awesome looking design.
My main sticking point at the moment is if I can get on fine with 8GB of storage and if it's worth paying £40 more for that extra 8GB. I've seen that Google Music is launching here in the UK at the same time as the Nexus 4, and since most of my current phone storage (of which I have 16GB) is taken up by music, that might be a great option. Then I have to work out if I have enough monthly data to stream the amount of music I'd want to listen to.
I'm really tempted myself by the Nexus 4 (currently running a Sensation). I've realised that with every phone I own I end up picking the ROM that makes it as close to AOSP as possible, so I might as well get a Nexus where that's your starting point. Plus, the Nexus 4 has the fastest hardware out there (maybe the Exynos scores 10 points more in some benchmark but for all intents and purposes I see the Exynos Quad, S4 Pro and Tegra 3 as more or less equal), quite possibly the best screen out there and what I think is a pretty awesome looking design.
My main sticking point at the moment is if I can get on fine with 8GB of storage and if it's worth paying £40 more for that extra 8GB. I've seen that Google Music is launching here in the UK at the same time as the Nexus 4, and since most of my current phone storage (of which I have 16GB) is taken up by music, that might be a great option. Then I have to work out if I have enough monthly data to stream the amount of music I'd want to listen to.















