In my experience both have their + and -.
If you are starting a new setup I would suggest going with in-vitro plants (tissue cultures). They are grown in highly nutritious substrate and have plenty of reserves. Tropica even has a 30cm in 2 weeks statement on some, and if given proper conditions they actually grow even faster. They are usually grown in higher humidity ( close to 100%) so the transition to submersed is easier. Another advantage is that you get many more plantlets from one pot... sometimes too many. The agar is easier to clean from the roots, thus you get plants with intact roots ready for your aquarium. You can keep them around for a few weeks until you can plant them. Depending on the source of the in-vitro cultures, they should be sterile, containing only the plant material.
However, the plants are very small. This means that you will have to wait some time for the plants to grow until your aquarium looks nice and it is difficult to plant from the box straight to an established aquarium ( more so if we speak about background stem plants). If you have lots of other high plants, the flow of water will be limited at ground level and the newly added plants might melt. In this situation potted plants might be better as they are higher.
I have nothing against potted plants, but sometimes the presence of BGA in the display aquarium, presence of sick fish in the shop etc. stops me from buying any potted plants. Some also suffer from a long adaptation phase. So if you trust your shop and are able to visually inspect the plants than go for it, if you order online definitely go for in-vitro
My last experiene was with introducing some eriocaulon sp. from in-vitro. Within one week it produced big roots a flower stalk. It is usually in very poor state when in shops.