First, I ignore the bars as it really doesn't mean much/as well as measuring speed using different apps. I go by my "perception" as to how long does it take to access internet, download apps, etc.
The voice reception has been good (live in the Twin Cities). 3G data speed is "fair" (slight improvement over the Hero) - 4G good (when I can get it). I do not drop calls, etc.
I am just not sure about data speeds when I roam (I really can't get this phone to data roam even though I know the settings are all correct - and I have done the setup correctly using other threads that address this issue - I have data roamed one time that is how I know it is correct). I was able to data roam with my Hero so I am not sure if there is a problem specific to certain types of towers (read somewhere about that), quality of antenna, software issue??? I personally have not had the LOS issue where I needed to reboot the phone, etc. I have seen the symbol but it corrects once it can connect to 3g (again it seems like it is this roaming issue?) - Others roam all the time, I can't get it to roam??
I have also noticed there is sometimes a few second delay when sending texts and I have had a few failures
Coming from my Hero, there some features I like about Sense and one just has to get used to this phone. Not real crazy about having to swype to answer or decline a call as well as how to make a call (more steps so really need bluetooth to be safe in the car). And it doesn't come with an SD card/plus getting used to how the phone identifies the internal storage as an SD card - so you have to make sure you know where files/pics, etc are going and move when you need to if you do have an external SD card (which can be cumbersome). Don't use the stock internet (downloaded Opera) - has problems accessing secure sites/not sure why.
But, there are also many good to great features of this phone: Processor is awesome, camera is great, "gorilla glass" for the screen is so durable, clear voice to name a few.
I will be honest, if the data speed does not improve with a maintenance release (therefore a software issue), I will not purchase another Samsung phone. I have read in many places that it may be the radio/antenna. For now, I don't feel the need to throw the phone. Good luck