Let me make one important generalization first. There is no such thing as the "perfect company" or the "best company to work for". To be more precise, you could label a company "the perfect company for me" or "the best company for me", but there are no "best trucking companies" or "perfect trucking companies".
Ask any member of any successful team, "What is it that made you so successful?" If they really understand the dynamics of any team, the answer is usually the same - "Having the right people". It's no different within trucking companies, which are indeed teams, although they may not always seem like it.
Home time is one of the most important considerations you should make when choosing a truck driving job. There is one point I can not stress enough – if you have a family of your own, please, please, please don't take an over the road truck driving job where you are gone for weeks at a time.
The larger companies have a huge amount of resources available. They have tons and tons of different types of freight and driving opportunities. They often have local jobs, dedicated jobs - where you remain with one customer or run one route all the time, regional jobs, and over the road.
Smaller companies, in my opinion, don't have too many advantages over the larger ones from a driver's perspective. You will definitely get to know everyone in the office, and they will certainly know you. Often times if you live nearby your main office, the people in your company will even get to know your family and the families of the other employees.
Dry vans are the most commonly found trailer out there. They are a big, empty box - plain and simple. No temperature control or anything like that. There are more dry van companies than any other type of company, and therefore you will find the broadest range of opportunities in this area.
You'll find that there isn't too much of a difference between driving for a dry van carrier vs a refrigerated carrier, but pulling a tanker or a flatbed is a whole different thing altogether. There are some significant differences between the lifestyles and the job duties of flatbed and tanker drivers.
One of the best ways, in my opinion, to really find out what life is like on the inside of a company you are considering applying to is to talk with some of the drivers and mechanics that work there. It's simple to do, it's incredibly effective, it makes perfect sense.