That's like asking "what car should I buy?" .... The best way is to test drive a lot of different models at a local dealer, and hopefully find a bargain. Fortunately the amp market doesn't get obsolete as rapidly as USB DACs, so you should find many bargains that are more than adequate. One issue may be that a lot of the new compact affordable amps nowadays come with a USB DAC function which is kind of obsolete if you already have a Mojo (e.g. Quad Vena, Cambridge Minx, NAD D3020 etc). You would want to get something fairly substantial to get the best out of the Mojo. Also if you want the simplest desktop solution without any fuss and cost then maybe a pair of active monitor speakers are better. The only things you need to be aware of is to make sure you don't turn up the Mojo's volume too loud, because the voltage goes dangerously high to fry a line input on some poorly designed amplifiers (that's why Mojo has a dedicated fixed line output mode).