Tough choice, and in all honesty I don't think it makes a big difference. Pros for stemless is you wont break your downstem and be fucked, and stemless bongs often have superior perculation in that first stage because you can have say a circ perk instead of just a diffused downstem. Cons- if the bowl breaks inside that joint your bong has a good chance to be cashed, compared to with a stemmed bong you can just replace the downstem and still keep the bong itself