This device comes in many varieties. No one type is suitable for every musician. So, your choice depends on your requirements, budget, preferences, and more factors. There are analogue and electric variants to choose from. However, electric ones are popular among the masses nowadays. They come in pocket-sized, clip-on, on-ear, or even decorative variants. If you search for the best brands, you can go for Korg, Seiko, Yamaha, Casio, and Roland.