Well I've been using unjailbroken and have ZERO (0, none, nadda, zip, etc, rinse, repeat) choppiness whatsoever. So maybe its not the OS, but maybe your phone.
Ok, first off it's not my iPhone 4, since I've done the following:
Restored as new, Restored from DFU, and even had the iPhone replaced at the Genius Bar.
Now, I've no idea of your ownership history when it comes to your iPhone, which version you have, how long you've owned it, or what previous versions of iOS you've used on the same device.
Anyone upgrading from an iPhone 3G, for example (not saying that's you), will think iOS 4.3.3 on the iPhone 4 is phenomenal because their previous experience on 4.0 - 4.2.1 was absolute hell.
For an iPhone 4 owner from launch, like myself, who's used 4.0 all the way through to 4.3.3 (and again, you could be the same, I can't assume anything), there is a clear difference in the performance from 4.0/4.1 to 4.2.1 and now onto 4.3 and it's incremental updates.
On a clean install, 4.3.3 is great. All the stock apps open as they should, nice launch transition animation, nothing choppy in the frame rate. Sync your iPhone 4 and load some third party apps onto it, and then you begin to see the problem. Now, keep in mind I'm not ranting here to prove a point or score kudos, I'm merely stating the experience I've had on TWO iPhone 4's and also in the Glasgow Apple Store display phones.
Apps ranging from Facebook to Engadget to Sky News to Sky Sports to TUAW to games like Infinity Blade, Real Racing 2, and in fact every single game I synced to my iPhone 4, do not run the launch animation. I could list all of the 200+ third party apps in my iTunes library and easily claim that NONE of them display the launch animation first time of asking.
You simply press the icon, it dulls, and app pops on screen ... whereas the stock apps behave as they always have. Sure, once an app has been loaded into memory, you can quit to the home screen, launch it, and get the full animation you would expect, but on first run it simply does not happen.
And, from time to time, you witness the occasional stutter in animations when launching Safari or Messages (from my own experience). It's minimal, it's over quickly, but it annoys the hell out of me because it detracts from the fluid user interface Apple is so infamously proud of having in iOS.
I notice it more because I'm used to 4.0 all the way through, although I will say that 4.3.3 is far less choppy than 4.3.2, 4.3.1, and 4.3 ... but I just cannot help but think either a) Apple have not told developers about the change in code and as such haven't optimised their apps accordingly, or b) it's a bug because Apple's own stock apps don't skip the launch animations.