What is a good beginner guitar amp to buy?

As a guitar tutor Im always being asked which is a good practice amp to buy.
Quite a few people have bought Line 6 Spider IV 15 Guitar Amp Combo.

Product Features 4 stunning amp models 4 channels of user-created presets 6 Smart FX (up to 2 at once) Tap Tempo, Bass, Mid and Treble knobs Drive knob, Channel volume,Master volume

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