I've never driven for them, so don't take my comments with a grain of salt, take them with the entire salt lick.
Landstar seems to keep its drivers moving, according to comments from Landstar drivers. They apparently have a relatively low turnover rate, especially for vans. Once drivers sign on with Landstar, they stay there. And I've never read anything negative on here about them.
They don't have a central dispatch. They use a series of independent brokers across the country that broker the expedited loads for the drivers. I have twice read comments from two different Landstar drivers that said essentially the same thing: it takes about six months for the various brokers to get to know you, and that once you get in good with them, they will get you plenty of loads.
OK, both times, the "once you get in good with them" bothered me a little. But then, since reading those comments, I have had three Landstar drivers, all van drivers, one former and two current, unsolicitedly tell me that if you sort of kick back a percentage of your loads to the broker, they'll make sure to get you loads. Drivers who don't kick back a portion don't get loaded as quickly or as often. The former driver said he got tired of pulling into a place, and then sitting there and watching drivers who came in after him get loaded out first, and he would only get loaded at the point where it was him or nothing.
This may or may not be true, all or in part, but getting essentially the same information independently so many times gives one pause. It does me, anyway.
It may all be true and the drivers there don't have a problem with it, or, as one driver put it, "It's just the cost of doing business." Like I said, drivers sign on there and, for the most part, don't leave, and you never read anything negative about them on here (including this post, which is definitely not meant to be negative). And it may only be a van thing and not applicable to straight or big trucks, but it is something that, I think, is worth investigating before jumping and signing on with them.