I feel your pain. I swore off Android after the Droid for the lag and the some of the odd things, like the SD card and music like you say. So why am I here now? I like the S3. BUT... your experience will vary. If you read the forums here, some users get HORRIBLE battery life and the phone lags. Fortunately, my battery life is good- not 2 day stand by good, but I can go a full day out, like 7am to midnight. And my phone will lag a bit, but it might be one swipe from one homescreen to another... once every other week. The samsung s3 is easier to use, but I still find putting music on it a bit of a workaround, even with kies. Much better than my Droid, but not as easy as the iPhone.
I've gotten into hot water over this here, but I'll say it again- the S3 is old. The phone is great, but Android evolves too fast to cling onto high-end phones that have been on the market for a few months. Especially as the HTC dlx (depends if you are on verizon) is coming soon and the galaxy note 2 (if you are into phablets) is also coming out soon. And given how most phones (if you don't root) barely get the next OS update, if that, the S3 is done for. Why? Why would Samsung put all their effort into providing Android 5.0 on the S3s and get nothing, when they can just sell the S4 next year with the new OS? And rumors are already making the rounds for the S4.
Now if you are the type who won't stroke out if a new phone is released 2 weeks after you buy your phone or plan to root your phone, then the S3 can be found for a good price, and it would be a good buy then.
In your position, I'd pass on the S3 and get the upcoming HTC phone or the galaxy note 2 (think of it as an S3 on steroids)
With the iPhone coming out so soon, might as well wait and try one out, why not? And might as well take a look at the Nokia 920. See what else is out there.