I prefer monitorS, plural... and typically with some variation in size, resolution, and display technologies.
My workstation right now has a very nice 27" 2560x1440 IPS in the center. Plenty of screen real-estate, high quality picture, ideal for just about any job... but MOST end users aren't going to have that and since I do back-end, front-end, design, and image manipulation I need to be aware of what it might look like for normal people.
Different display technologies run different colour gamuts, and there's nothing worse than -- for example -- making a beautiful design running multiple shades of tan on a IPS, only to have people on cheap displays bitching about the purple striping.
Hence my right display being a 24" 1920x1200 reasonable quality Samsung, and my left display being a 24" 1920x1200 el-cheapo Envision.
I end up with all the desktop space I could ever need, and I get an idea what other people are going to see.
IN GENERAL that's a mistake a lot of developers make is creating their workstation to be nothing but top of the line bleeding edge tech. From the CPU, to the graphics card, to the displays. *Normal people don't have these things!. It's often better to do your development on what "normal people" would have so you don't paint yourself into a corner with things a "normal computer" can't even do.
Hence my workstation having three displays of varying quality and price, running a Celeron J1900 as the processor (with it's whopping 10 watts of power draw), and a 5400 RPM laptop HDD as what 'work' is run off of. (regularly and automatically backed up to a RAID 1 on the network). It gives me a better idea what Joe Sixpack and Susie Sunshine can expect from my results... It's "cheap by design"... and why I have $$$ to have my media center / gaming rig be pretty sweet.
Overall though, don't cheap out too much on your displays, your keyboard, or your mouse. If you're going to be developing code that's where 99% of your time will be spent, so choose wisely. Treat yourself to at least one good IPS monitor. Treat yourself to a decent mechanical keyboard. Treat yourself to a thumb type trackball to reduce the strain on the wrist. Treat yourself to a quality mesh-backed fully adjustable chair that can breathe.
In four to eight years your eyes, hands, and tuchas will thank you as you watch your peers bitching about carpal, changes in prescriptions, and visits to the quacks known as chiropractors.
Oh and for the love of Christmas, think in terms of comfortable seating position for your monitors -- aka 3 to five feet. If the text is too small bump it in the OS (and any program settings for those that don't obey the OS). Do NOT hunch yourself over the keyboard plastering your face inches from the display. If you have to do that there's something wrong with your display, your OS/program font-size settings, or both.
For example, if you're using a keyboard tray, and with your arms outstretched normally to the keyboard (elbows at an obtuse angle, NEVER acute!) with the tray all the way out, you have trouble reading the display or the text feels too small, move the display closer away from the wall, increase the font sizes, or get a bigger display with a lower PPI.
There's a lot of ergonimic hoodoo -- but an equal amount of stuff that just makes sense. Given the sedentary lifestyle and host of health issues that can arise long-term from it, spend a few bucks now to save yourself on medical bills later.