There is always the classic caldron shape (i.e. duo qiu) that is an all ‘round’ solution for most infusion conditions.
The popularly seen caldron with the domed lid is an all time classic because of the all round infusion capability it has. This is a great style for green, black, fine leaf puers, and beaded Oolongs, such as Tieguanyins.
Well-considered ergonomics, superb spout flow, and precise crafting are basic in ALL acceptable quality Yixing teapots. The neck of the lid fits perfectly into the collar of the body. The lips of both are so flatly against each other that there is a vacuum pull when you try to open the lid. Leveling of the colar of the pot is instrumental in gongfu tea infusion when water is filled to the rim, and the underside of the lid neck is used to scrap the surface of water before covering the pot for tightness.