She's ready (overdue she says!

Yamaha YSL-640
Bach 36B
She plays a few jazz / big band groups, and a few performance bands, usually 1st trombone.
We can get a good condition used Bach for about the same money as a new Yamaha.. We were being tempted by some of the "refurbished" Ebay horns from the USA, but after googling the name of the seller, have settled either on a new Yamaha locally, or an excellent condition vintage Bach from a reputable store like Dillons.
Is there a right answer here? We're seeking subjective opinions on which of the two is going to be better suited to jazz or performance play, and this community seems to be the best-frequented trombone one I can find online.
The usual answer is probably "get your ass to a music shop and try them", but here in Australia all the shops I've tried don't carry actual physical stock of higher than student grade trombones, and we don't have the kind of customer service North Americans are used to.
Lastly, on the new vs used - we're not averse to buying instruments which need a good service to be "right" (we have a mix of new and vintage sax's and clarinets in the house too), so this is really about the playing / sound / enjoyment of the instrument.