Now I know that could just be some water/moisture but it could also be poorly purged BHO.
On topic:
There isn't anything that will compare to a proper rig as far as efficiency and durability/longevity goes. If you have no other option, melt a small amount of oil on top of a bowl of flower and smoke it. Hot knives work but make quick trash out of your silverware.
Oil pen for sure. None are that great so just getting a no-brand one that's cheap is generally the best option. 510 battery, charger, and globe atomizer is really all you need. About the cost of an oil change around here.