The answer to what is best will depend on your use. What do you want to accomplish, how far do you want to talk,  terrain you are in, budget, etc.  

The system I have is VHF simplex.  We can talk mobile to mobile 5 miles all the time, sometimes up to 15.  It is me, my son in law, and a friend occasionally helping.  We carry cell phones and have acceptable service most of the time.

 A friend's business involves 3 office staff, 2 service men, up to 5 delivery drivers and 2 transport drivers covering all or parts of 6 counties.  He has UHF trunking radios and rents use of a commercial radio system. Because he is handling a hazardous material any of his people have to be able to  reach the office as well as anyone else at any time and everyone can hear what is happening.

My system is best for me.  His is best for him.   There are other ways of doing it.  So in order to answer your question you are going to have to tell us more about you and your use. 

Edit: I side stepped the first question.  The simple answer is the frequency used.  While being honest, it does not really answer what you want to know. Let's start radio class ...

Typically VHF radios will be talking directly to each other (simplex).

UHF radios will talk to each other through a repeater (duplex ... technically half duplex but that's getting too deep too fast).  You may own your own repeater, use a community repeater where everyone can hear everyone else,

or a trunking system where you don't hear anyone but your people and nobody else hears you.  You can talk long distances if the system is in place.

images from http://bsar.org/manual/communications