Like plants, rock is a personal choice. There are different colors and sizes.
It is nearly impossible for landscapers to carry samples of all of the different colored and size rock that is available. Some might have small samples with them but getting an idea of which one a customer will like is difficult.
Many times rock yards will allow people to vist them and if they ask take samples. Consider bringing zip lock or shopping bags, pen and paper (to label the samples) to a rock yard. When you get the rock to your property we suggest that you put it out, wash it off and let it dry since it is probably dusty. Once you do that you might get an idea of which color or colors you like and which size.
Keep in mind that you are not limited or restricted to one color or size rock.
A ton of river rock is typically more expensive to purchase than "normal / common" rock and the price can scare some people. Keep in mind that the amount of rock many people need at residential properties will not affect the final price by a lot. In many cases it might only increase the cost by a few hundred or a few thousand dollars and if you feel it would make the landscaping look considerably different or better it might be money well spent or use it in select areas.
It depends on a few factors including
Wood mulch is an alternative to rock as a ground cover and like rock has benefits and drawbacks. Some people like keeping rock back from around plants and some wood mulch can be purchased by the bag or in bulk. Just like rock, the size and color of wood mulch varies.