My two favorites are the Herbalaire Elite and the Ariser Solo. Both can be used with a glass bubbler or water pipe, given the right attachments. The Herbalaire Elite comes with everything you need but the bubbler/water pipe (14 and 18mm I think.) I also have a Volcano, Arizer Extreme and Storz-bickel Plenty (along with a bunch of garbage), but I don’t really use them. Those last three work well enough, but aren’t my preference. The Extreme is kinda slow heating. The Volcano is great if you like bags and parties (Herbalaire does bags too.) The Plenty is kinda goofy; I didn’t like the way they chose to make it operate.
In my opinion, most important feature is the ability to expose the herb to highly temperature-controlled hot air from the bottom. All the ones I listed do that. I spent a great deal of time buying and testing vaporizers to determine what was best for me, and that was the result.
The cheapest you’ll find from my list is the Arizer Solo. It takes a little getting used to how it operates, but it’s a good buy and properly heats the herb. It’s also highly portable, being battery operated. The battery is rechargeable and replaceable. Have not tried the Air, Air II or Solo II, but they’re basically the same with subtle differences in features.