Depends on the purpose.
If you want professional typographic printing, you need a printer with Postscript.
Search Genuine Adobe Postscript 3 printers.
If you need more speed photo-quality printing - PCL6, but it is subject to errors - PCL XL error.
In some cases PCL6 much slower than PCL5.
In PCL6 also lacks some features PCL5. If you do not want any trouble, use PCL5.
Briefly at the other parameters being equal:
Quality: Postscript > PCL5 > PCL6.
When still need PCL6? If you need a complex photo-quality printing. Then maybe you'll get some pluses.
HP Page Description Language
Choose printer consumables cost in terms of its full-time operation. This will reduce the cost of printing several times.
Avoid universal devices for printing.
HP Officejet Pro 276dw: HP PCL 5, HP PCL 6, PS3.
Convert PS3 to PDF 5.
HP Officejet Pro 8600: HP PCL 3.
If the choice of these two devices is better to take HP Officejet Pro 276dw.
Keep in mind that most likely will be emulated Postscript via PCL.