the best one that i have seen is a brady labelmaker. The printer itself can connect to a computer for all sorts of fancy label making, but in terms of suitability for electricians it is amazing. It prints wire numbers on inserts for sleeves and will serialize/increment them, on heat shrink tubes, and magnetic pushbutton labels are available.
On the spools for the material to be printed on, it also featurs an id chip of sorts that contains the details of how much printable room there is, etc which makes it easy to change spools without worrying about settings.
it came in a heavyduty case, with a mains charger/adaptor and is also battery powered.
For most of my work in labelling panels, switches (where required) and outlets, I use a Brother Label-maker, it is ruggedly built, rain-proof and is quite easy on label cartridges, provided you don't try and write a novel on each label.
I think Mike and I have the same simple $30 label maker. It's perfectly adequate for marking panels. You'll uses scissors pretty often to trim the labels, and the label adhesive usually works pretty good.
Where it falls short is for marking wires, etc. The adhesive just isn't up to the demands 'outside the panel.'
The big advantages? Label tape is cheap, and can be found in any office supply house. While the Brady and Panduit printers have more functions, and better tapes ... so far I haven't felt the improvements justified spending the 5X higher price.
I have Casio, Brothers & a Rhino (Dyno) Casio easy to use, labels ok for panels but not for wire or most other surfaces. They will fall off after short time. Same for the Brother but somewhat harder to use. I got the Rhino free with the purchase of 10 labels. Works great. The cloth labels will stick and stay on most any clean surface including wire. They make heat shrink labels and the menu has electrical, telecom and data symbols. Labels can be bought every ware. I like the Brady also. The Rhino is a good lower cost alternative to the Brady.
The Brady that bindi called out is the one I would go with but it is not cheap. It does a thousand different things from wire numbers to huge banner type signs and bar codes even. You can choose from many different types of labels and colors.
I haven't gotten into much wire labelling yet, but I like Panduit's sheet of plastic labels you can wrap onto wires and cables. You can hand-write or run them through your printer. I've used it in the past and like them.
I'd say if you have the need and the coin for the Brady, then that’s great. I use a Dymo LP300, which prints 1/4”, 1/2” and 3/4” wide labels. The 1/4”are great for data ports and labeling switch and receptacle plates. The 1/2” is what I use most for labeling J-box covers, panels, disconnects and just general labeling. The tape cartridges aren’t too expensive and come in lots of colors, but I primarily use yellow, white, silver/chrome and clear. For labeling wires and terminal strips, I just use the pads of Ideal cloth backed sticky labels.
I also still have one of the old Dymo/Esselte 1570 embosser type labelers. It still seems to be the most durable for long term labeling under some conditions.