a road bike that costs under $1,000 will typically have sora shifters or maybe tiagra shifters if they are shimano brand. The derailleurs will match accordingly. Soras dont shift well and I just found out they actually made a shifter below Soras and I wonder how much lower is the bike industry willing to go? Any bike that costs under $1,000 is usually a piece of junk. Ofcourse you can ride the bike but they are not built with care like anything atleast $1,100.
My standard is that you have to spend atleast $1,100 to get a decent bike.
A bike that costs $1,100 can and might have shimano 105 components. They shift much faster and smoothly than tiagras or soras. I think this is the minimum you should get if you are going to spend a lot of time riding your bike. Some bikes in this price range will have tiagras depending on the company. You need to pay attention to the components when buying a bike in this price range.
A bike in the $1,800 range will either have shimano 105 components or ultegra components. Ultegra shifters and derailleurs are butter smooth when it comes to shifting. And they definitely shift fast and flawlessly as long as the bike is tuned properly. 105s work just as well except they are slightly less fluid during gear changes.
If you spend over $5,000 then you get Dura-Ace components which are the race level components from shimano. Between $1,800 up to $5,000 you are paying for the quality of frame and perhaps even the quality of other features on the bike.
To get a carbon frame bike you will spend around $2,000. Carbon frame is stiffer and lighter. They make the ride feel fluid and smooth. However they are unforgiving on potholes because the stiffness can make the irregularities quite jarring. When it comes to road abnormalities, aluminum frames can absorb them far better than carbon. On perfect roads carbon frame will absorb everything and make you feel like you are floating. Also typically carbon frames will be a more efficient platform for efficient power transfer. your efforts on pedaling will go directly go through the drive trains rather than being inefficiently wasted on a pliable and forgiving frame that is mushy.