I would wait for a while till we get the nexus devices in November etc. and then we should be getting a range of new phones by LG, SE, motorola as well, which all look very promising (on paper they look better than the GS 3, X and S!) and also should be getting the one XL, which has the 720P IPS screen of the X and the same design as the X, but has the S4 chipset instead of tegra 3, so it will be much better than the X especially in battery life, which supposedly is the best currently (better than the GS 3 and S).
But if you have to buy now/soon:
The one S/X and GS 3 have their strengths and weaknesses, they are more or less the same regarding the camera (for photos), audio (for the S and GS 3), battery life for the S and GS 3
Essentially you get the GS 3 for these reasons:
- SD slot
- removable battery
- best 1080P recording in terms of light metering and smoothness
- lovely 720P SAMOLED screen
- NFC
- great NLED
- great battery life
It is the most complete package currently.
You get the one X for these reasons:
- great IPS 720P screen
- design (subjective)
- sense V4 (subjective again, the gallery, camera, calendar etc. are far better than touchwiz alternatives and any other 3rd party app IMO)
- NFC
- the camera is great in terms of features/options and the UI
You get the one S for these reasons:
- S4 chipset, the best there is (the dual core is better overall compared to the quad in the GS 3 and X) excluding the new iphone 5 A15 dual core iirc
- amazing perceived/build quality
- design & size (subjective)
- great battery life (just edges the GS 3)
- sense V4 (subjective again, the gallery, camera, calendar etc. is far better than touchwiz alternatives and any other 3rd party app IMO)
- the camera is great in terms of features/options and the UI
As to which screen is better between the X and GS 3, that is up to you, many think the X screen is superior and vice versa for the GS 3 screen.
Iphone 5:
This will completely come down to whether you want/like iOS over android.