In my opinion, a VTC that would appeal to me would be one that focuses on realism and the every day operations of a transport company. The people running the show need to have a fairly decent background when it comes to transport companies to determine what is and what isn't classed as realistic. They also need to be active and participate with their drivers and provide the drivers with opportunities to develop and move up the ranking ladder within the VTC (goal setting, etc). The virtual paperwork is no issue and as long as they accommodate a program to aid with it (either TruckBooks or an independent program) then it's almost all automatic anyway and requires little to no effort. The VTC should have a professional page on the forums that describes what the company do, where they are based from, the fleet of trucks they have and the company livery (which shouldn't be too 'out there') - all of which should be headed with a clean company logo.
A lot of VTC's (when I used to play all the time, unsure if they've changed) are heavily focused on convoys. That's not an issue at all, but I for one am not interested in large planned convoys and prefer to drive alone or in a very small group. When they're more bothered about convoys than how their drivers perform or their activity then it drives me away from the company.
Professionalism and the fun factor is hard to balance because all members will be different and have their own tastes which is well within their right. In my opinion, VIVA have got this down to a tee. When I drove for them they held regular convoys for those wanting fun, and also recognised people for their realistic approach to trucking - a lot of the divisions incorporate roleplay into their delivery logs which was great to see (all of which was optional to balance to realism and fun). They regularly updated their special delivery lists and also held daily polls etc to keep the community engaged which really helped balance the two factors.