I have used both, and much prefer the bottom pour casting pots. The secret to using both and get good balls is to have the mold heated, and in the case of a dipper, to keep it HOT, too!, and then put the mold as close to the pot as possible, so that you limit the cooling time that affects the dipper and the lead in it while moving from the pot of lead to the mold. With the bottom pour pots, you need to get that mold as close to the spout as possible so that the lead does not cool too much before it gets to the mold.
Cool lead results in wrinkled lead balls and bullets, rounded grease grooves, instead of full, sharp-cornered grooves, and sometimes, rounded bases in base pour molds.
I did very good work with a dipper when I used one, but I didn't like the lack of control due to needing a longer handle to keep my hand away from the heat of the pot to hold both the mold and the ladle.
With the bottom pour mold, I used a steel block- made from scrape, to rest the mold on high enough to have the sprue cutter about 1/4" below the spout. It was a simple matter to slide the mold on that block of steel under the pot, line it up with the spout, and then open the spout with the arm from the pot. For me, the bottom pour pot was a much easier and faster way to make balls and bullets.
Wear gloves with both pots, to protect your hands from heat, and from any splashes or pops of lead from the pot. You only need to have ONE small drop of molten lead land on your hand or wrist to learn why this is the most important safety rule to abide, after wearing eye protection. Please don't ask me how I know this!