For USA users, the international version's downsides are:
1. No LTE. In general, you always want the fastest connection speed possible. I've seen LTE and it's a quantum leap in end user satisfaction when surfing the internet, etc. Esp with streaming videos. Big deal for most people, even if you don't think you'd need it. I never thought I'd need anything beyond a standard DSL connection, but I went with a cable modem connection (on a free trial from comcast) and it makes a huge difference. And LTE doesn't add any cost to your monthly plan in the USA.
2. Cost. No subsidy. So what would stink is if you used your international version for 2 years anyway on AT&T, and you never got the subsidy. If you're going to be with a telephone company for 2 years anyway, it's like not taking their freebie.
3. Maybe battery life issues. Quad core may eat into the battery (then again, LTE may eat into it worse).
Reasons for USA owners to get international version
1. Higher resale value
2. Faster updates, and probably a more stable, better overall user experience
3. Likely a truer experience, crapware is really a huge problem from the carriers.
It's a real hard choice. The fact that faster updates is only available with the international version is a big deal, that is in a nutshell everything that is wrong with Android. You're not buying an Android phone.You're basically buying an HTC OS phone, or a Samsung OS phone. Because you're at their mercy trying to upgrade to the latest functionality. With Windows phone and iOS, you get updates, regularly, easily, and reliably. Something so basic,hasn't materialized on Android.
If the branded versions had updates within 2 weeks of release from Google, then the appeal of an international version would go away alot for US users. It's a sad commentary on the state of Android....although I'm going for Android anyway b/c I willingly know that I am going to deal with poorer stability, more hassles, and do it all for the sake of "open source" (although I think android is more closed than we'd like to believe) and I want better hardware choices. The more I think about it, the more I realize that Android's runaway success has to do with carriers more than it has to do with satisfied customers.