At this point i mostly raise Portulacaria, which enjoy being partially rootbound (in my experience). I've got many in pots, big and small, and several dozen in the ground. From what I've seen, when I put a plant in a big big pot it just pretty much sits there as the roots colonize the pot. Once the roots hit the bottom, then it starts growing like mad! However, the plants in the ground seem to grow roots forever before top growth... the ones in bigger pots have a lot more diameter growth. We're talking cuttings here, I've not put a "real" plant in the ground yet. I do know Jim Smith has one in the ground, and it's HUGE... it's also been there for quite a while compared to my sparse 15 months for my cuttings.
For plants that don't like being rootbound, I'd vote the ground in my area (if the soil is decent). Why? Well, first off the temperature of the roots doesn't fluctuate as much as it does in a pot-feel the soil in a pot and then go the same depth in the ground. Down here in Florida, roots can easily get overheated in pots-takes a lot more to overheat in the ground (not to mention the roots will grow to cooler areas). Water level is more consistant too, overwatering in the ground would be alot harder than in a pot.
However, it does take a lot more water in the ground to reach the same degree of "wetness" than it would in a pot, something to consider when under water restrictions! Rain seems to be a distant memory around here (which means we're going to get walloped when it does start)....
So, I'd say, for any species that likes being a bit rootbound, go for the bigger pot/box. For anything else, the ground with decent growing soil
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