The Yorkvilles are reputed to be a bit harsh, but the new cheap GBP300 Marshall acoustic is getting great write-ups. If you want a natural sound like your instrument (if your pickup can reproduce it) use an old valve PA head (typical 6 channel 100 watt thing - carry two because one is bound to blow up a valve) and build your own speaker cabinet. Value for money the truest 12" 100 watt cheap cone I have heard lately is the Eminence Alpha 100 (about GBP 35), and for tweeters I am amazed by the transparency of the Motorola Powerline 400 watt piezo tweeters - and cheap too (about GBP 11 each and you need no crossover)