Human: What are the most popular types of e-cigarettes and vape pens? Assistant: 
The most popular types of e-cigarettes and vape pens include tank systems, mods, pod systems, and disposable e-cigarettes. Tank systems typically have a larger battery capacity and allow users to refill their own cartridges with different flavors. Mods are more customizable than traditional e-cigarettes and come in many shapes and sizes. Pod systems use pre-filled pods that contain nicotine and flavorings. Disposable e-cigarettes are designed for one-time use and are often sold in packs or cases.