"Is there a difference in effect?"
Many different forms of vaporizers exist and the technology and engineering can be complicated. Flowers, concentrates and oils can be vaporized. For starters, it is important to think about what you are vaping. Is this a clean extract? Are these flowers free from pesticides and chemicals? Vaporizing involves heating the substance to a temperature above the melting point, yet not high enough to cause combustion. Basically when one vaporizes flower, hot air is moved across the flowers, and essential oils and compounds are melted and released into a gaseous state, which are then inhaled. Vaporizing concentrates and oils can be acheived in a number of ways. Usually a heating element or coil is utilized to heat the oil or wax or hash or shatter. Often you get what you pay for, and cheaply made vaporizers may be constructed with poor quality materials and there is some concern about metals being released from the coils.
There is a very strong distinction. First off, most concentrates are going to be a stronger and more intense high. Flower vaping is very smooth and the smoke combustion is not nearly as harsh as inhaling marijuana smoke through a water pipe or a hemp paper.
Any concentrate is form of extraction and is normally between 40-70% THC. Most top shelf flower is between 20-28% THC.
But ultimately, its depending how strong you would like to dose yourself with. The vape scene in the marijuana industry is quite competitive, specifically in the oil. There are solvent and non-solvent products. There are multiple types of terpenes that are added to these oil vape pens to give them all natural flavors extracted through plants.
Personally, I like Dank Tanks. They charge fast, discrete, economical, and hit strong. I can charge the charge anywhere in my car, computer, or a wall because its a USB computer charger. The oil conserves the marijuana taste and has NO ADDED TERPS, to preserve the taste of the marijuana plant.