Now, as for which phone to buy, that is a loaded question!
Galaxy S4 is probably the best of the Android bunch. Why? Its processor is slightly better than HTC One because Samsung overclocked it. The screen is, arguably, the best right now, surpassing HTC One in most respect except for full brightness. It is also (unofficially) the toughest & most water-resistant phone...see Youtube video:
??? S4? ?? ???? ??? ???? ???! (GALAXY S4 Reliability Test) - YouTube
I hope that you have held the GS4 because I thought that it looks/feels better than my Note 2 and GS3. In addition, outside in good light, GS4 has the best camera to date. (iPhone 5S will likely dethrone it in the future.) Lastly, as per Samsung, GS4 will get a software update in the near future where you can push "some" apps to SD card which allows you to free up internal memory. Remember, the app itself must allow you to do this for the feature to work. (As you may know, ever since Android 4.0 ICS, this app-to-SD feature has been deleted for security reason. So, it is nice to see Samsung bring this feature back on their phones.)
HTC One is a good phone but the problem is that it compromises too much on certain things. HTC camera is arguably the most useful at this time for Facebook/Twitter folks. However, it is also the crappiest camera in good light due to the low MP count...you can't get around that. The design itself is near flawless and of high quality. The speakers are great. The problem is that HTC is under a lot of financial stress. Their engineers and top execs are dropping like flies!! Why is this important? In the past, I would recommend HTC because of their software updates etc.. This has not been the case recently where software updates are rare to come by and their older phones get abandoned. This MAY be different with HTC One...because this is their flagship and they "promise" that this will be different. Time will tell. It has no SD card nor replaceable battery...the price you pay for an all aluminum chassis.
Sony smartphones are nice, but they always seem a step behind! Not sure why given that Sony has a big budget (unlike HTC) and apparently works closely with Google on a lot of things. I believe that their top phone is still using last year's processor (S4 PRO)...WTF?! Their screen technology sounds impressive (Bravia engines, etc.), but real world testing is lackluster. Their camera is supposed to be excellent...look at what Apple iPhone can do with Sony's sensor! But, again, somehow, despite 13 MP etc., Sony camera just doesn't add up. The other problem with Sony is that Sony has not shown that it will support their device in a timely manner.
Apparently, there is a new Sony flagship coming out later this year...called Sony Xperia i1. This will have the S800 chip (top dog for 2013) along with point-&-shoot rivaling camera. I know that Sony can make great cameras in small packages (see Sony RX100). So, I am hoping that Sony has learned its lesson and go full blast with this Xerpia i1 phone.
Unfortunately, none of the Android companies are as diligent as Apple in providing timely after-sale software updates. Samsung is probably the best right now.
I save the best for last...let's talk about Nexus and Google Edition phones. IMHO, if you're going to go GSM ST (which I HIGHLY recommend), then I would go with these phones!! For one, these phones get the quickest updates...near Apple like! The software updates will be better than other Android phones...because it does not have to go thru the manufacturer nor does it go thru the carrier (biggest slowdown point). I am particularly interested in Google Edition phones (HTC One and GS4). Remember, you have to buy these phones at full retail pricing. B/w the two, I would pick GS4 Google Edition, even though it costs $50 more than HTC One Google Edition. Now, if you want to keep things cheap, then get the Nexus 4, which is a pretty good phone for the price. Still, I would get GS4 GE if money is not tight. Rumor has it that Sony will soon make an Xperia Z Google Edition too. Again, I would still get GS4 IMHO.
The only phone that would sway me away from GS4 is iPhone 5S. So, you may want to wait for that (if you can). iPhone 5S is Apple of course...but with the new iOS7 and upcoming camera, it should be pretty good. Recent iPhone cameras have been class-leading (if that is important to you). In addition, later this year, Samsung will make Galaxy Note 3, which should have the latest and greatest Android stuff (camera, S800/Exynos 5 chip). Note 3 will have stylus (same as my Note 2) but it will be as big or slightly bigger than Note 2. It is a big phone, but the tradeoff is that the screen is huge and thus you don't get eye fatigue looking at it for a long time.
Basically, if you can hold out till October, then you will have badass choices!
Sorry about length...and Good luck.