I used to play clarke sweet tones, nice whistles and perfect for learners, easy on the pocket as well. If its a bit more upmarket you are after, then the Rose as mentioned above is nice. Personaly I use the Overton, again not cheap, and if required you can purchase the tunable type.
For volume..the Susato is probably the loudest and not too expensive either, goes for around the same price as the Dixon also a nice whistle.
I dont like the chieftan whisles at all.