I use a Brother QL-500 and P750W for labels. Mainly because they've never failed me and the editor software is fairly powerful (generates labels from spreadsheets and databases) and seems easy to use. But then I haven't used anything else in the last 10 years, so no idea what the competition is like.
When the QL-500 eventually fails (I bought it in 2008) then i'll just replace it with a new one - there seems to be about a half-dozen models to choose from.
And like woody, I use barcodes no problem. Just tried the QR, MicroQR and Maxicode (for shipping) - all work fine. There are 18 and 24mm TZe tapes available for the P750W, but no 21mm wide.
Avery make great labels, but I haven't tried their latest software (Design&Print) - but this might be do the 2D barcodes etc.. This will certainly be the cheapest way to mass produce these labels.