AER the obvious choice, but expensive. I play fiddle, amplified and unamplified and I'd strongly advise that a decent pre-amp is the most important thing. It will load piezo and similar acoustic instrument pu's correctly. Any reasonable small keyboard combo will suffice with a properly pre-amped signal and it will sound much better through a PA, too. Guitar amps are not ideal - they have built in mid-boost, which makes a fiddle sound very harsh. I use a Fishman pu and a preamp made by the firm that makes the Sessionette amps. Works very well. There is a German-made fiddle pickup that is mounted in the sound post, which is fabulous - can't remember the name offhand, but it's not cheap.