Hello Sally, there is no correct answer to this question. Lifestyle, budget and personal preference play a role.
If you are a homebody, the good old Pari Dios tabletop compressor machine, about the size of a tissue box, is a very durable and inexpensive choice. It is also the primary machine paid for by Medicare and some health insurance policies. The downside is that it is somewhat loud, and takes about 20 minutes for each 4ml vial of solution.

If you need a more portable Unit, there a a number of smaller, lighter compressor machines, some that can run on battery or cigarette lighter. These are quieter, but tend not to as durable and usually not covered by Medicare.

If you want fast, quiet, and no tubing, there are impeller run machines, battery operated. You inhale directly through an attached mouthpiece. These vary widely in durability and cost and are only covered by insurance for a few specific inhaled medications.

If you need something highly portable, this is the obvious choice.

The best way to find out what you like, try to get an appointment with a respiratory therapist to test a few machines.

I think this is a very individual choice. I like the Philips InnoSpire Go, but it only lasts me a year or so. The Pari can run for several years.

Sue