Have you found anything that indicates what the specs of the S4 might be? I haven't even seen any rumours regarding it so its impossible to even say how it will compare. Will it beat any phone out today? Of course. Having said that, you can always wait for the next best phone, but you could be waiting as long time. If you want a new phone now then either the S4 or Onex+ make for as great choice. Both have been out for a while and you can read all about their pros and cons, specially on this site which has a large user base for both phones.
Past Devices: Google Nexus One (sold), Samsung Galaxy S2 (sold), B&N Nook (returned), Samsung Galaxy Tab 7 (sold), Samsung Galaxy Tab 10.1 (On the Shelf)
Current Devices: Samsung Galaxy S3 (AOKP), Nexus 7 (Stock), Chromecast