5 gallon containers are small enough to stunt a plant over a good season of growth there, but another plant is still another plant. Put the annuums in the buckets since they use less water, but even in the ground you may end up wanting to water them a few times over a season so if the plot of land is distant from your water, consider how much effort that will be, although it's probably going to be a lot less effort than more frequently watering of plants in buckets.
If the plot of land is high clay then consider starting a compost pile. This is a great time of year for that to include yard debris like leaves, twigs, pine needles, grass clippings, etc. If you till it in this fall then it'll break down a lot by next spring, but even doing that next spring and again every year will help, as might growing a cover crop you till under.
One other thing buckets can do for you is that if you have them over concrete or gravel, I mean a fair amount as a buffer, that can decrease insect infestation, and having them closer to your house can deter animals from eating them, especially if you're outside enough that they see or hear you every now and then.
