Box mods (assuming they're variable voltage/wattage) are definitely a better choice for cloud-chasing than mech mods.
With a mech, you need to build your ohms to suit the "cloud-chasing", meaning you need to build .5 or lower if you wanna really kick out the clouds. With a VW/VV device, you can build .8 ohms and then adjust the wattage to give you the clouds that you want.
I run my OKL-T20 box mod at about 4.5V with a .6 ohm coil in it, and it puts most .3 builds/mech mods to shame.
ETA:
If you're entering competitions or whatever (and let me say straight-up: that's dumb) they usually have rules that only allow one 26650 or 18650 battery device, meaning box mods are generally off the table entirely. Just so you know.