Honestly this is one of those questions where you really need to go beyond just Google ratings and check actual traveller reviews on forums like this one.
From personal experience and what most group travellers suggest, look for companies that have been operating for at least 5 to 7 years, have GPS tracked vehicles, provide well maintained AC tempo travellers and assign experienced drivers who know mountain routes, especially if you are planning pilgrimages like Chardham or Kedarnath.
Three things to always check before booking, are the vehicles regularly serviced, does the driver have hill driving experience, and are the final rates transparent with no hidden charges for toll, parking or night halt.
Delhi Tempo Travels is one name that regularly comes up in travel communities for outstation and pilgrimage trips. If you search tempo traveller on rent in Delhi you will find their rates, vehicle options and customer reviews to compare before deciding.
Hope this helps!
