So the nightstand is the only real change? OK, desk in the last one. I can't say that any make a real impact.

These options are quite bland and inoffensive. Is that what you want, or do you want something that makes more of a design statement?

If you use the office more than an hour a week, a lot more needs to go into the desk and storage.

If you'll be using the room as a home office 8 hours a day, five days a week, then consider a Murphy bed for the occasional guest, and a serious desk at least 30 by 60 inches with drawers. Add a file cabinet, printer stand, and a very good chair.

I️ have a few ideas:
1. I️ agree that some more storage is necessary for work space, maybe a bookcase of some sort
2. What about putting a sofa-bed instead of the queen size bed? American Leather makes great sofas that are not the old style springy-very-uncomfortable fold out beds (probably more affordable than a Murphy bed)
3. Looks like the only thing changed in each photo is the nightstand and I️ like the first one best as it adds some warmth due to the walnut wood color

I'm in agreement re the first nightstand giving some warmth. I think if you choose the last desk, though, getting a nightstand to match (not the one shown) makes sense. Accessories will be important here, in either case, to give your minimal look some dimension.

If the room will be used as a guest room frequently and a full bed is needed, consider a murphy bed. If only a twin bed is needed, consider a day bed that could be used as seating by day and bed by night.

If the room is going to be used as an office regularly and guest room occasionally, consider furnishing it primarily as an office -- but sparsely furnishing it, leaving room to move some furnishings to the side and add an inflatable mattress in the size you expect to need when the room is to be used as a guest bedroom.

What furnishings you use for the office depends upon individual need and taste. One thing I'd specifically recommend: A two drawer filing cabinet with third shallow top draw for pens, etc., could double as an end table.

To maximum the storage, think vertical ... get as much storage as possible taking up as little floor space to do so as possible.

Choosing furnishings with castors -- or adding them -- can make changing the use of the room much more convenient and, for that reason, I'd recommend against the bed you've chosen.

You should be able to get a really good quality metal bed frame with castors that can adjust to be either twin or full for about $64 last time I priced them (a couple of years ago). A headboard is going to make your office feel much more like a bedroom.

If you're going to choose a frame w/headboard, consider choosing one with storage built in beneath it. There are less expensive versions of this Lowell Captain's Bed:

https://www.google.com/search?q=images+full+bed+w/storage+built+in+beneath+it&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwjng8W7iffXAhXHQyYKHS3eAaMQsxgIKA&biw=837&bih=514#spd=14987280754496422807&spf=1512621305210

Thank you all SO much for the thoughtful responses. Lots of great points. It sounds like I need to give more details on room usage, so here goes --

Guest room usage: We have family over like once or twice per month and they stay a few days. My wife insists on there being a queen bed in there for guest comfort so I don't think I will be able to change her mind on that.

Office usage: It will be my place to retreat to late at night for a couple hours most nights after everyone has gone to bed. I will either get some work done, watch a show, or play some guitar at the desk. I have an office at my workplace that I commute to daily, so this room is by NO means a full-time office.

Storage needs: The house has a lot of storagein closets so I'm not too concerned with maximizing under-bed storage or filing cabinets.

My point is mostly to make a very aesthetically pleasing, minimal, and stylish room with kind of a light palette. I totally agree some artwork and accessories will be needed to give it "some dimension."

Sounds like most of you like the white desk. @studio10001 I'm curious, you said the white nightstand shown is no good? It's from CB2. Any alternatives?

I'd Iook for a less wide choice. It will mimic the desk drawers better as well as provide some contrast with the many horizontal lines going on.

If I was a guest staying a few days on a regular basis, I would appreciate a night stand with some drawer or shelf storage for my nighttime reading book, eye glasses, hubby’s wallet and watch, and our mobile phones with outlet to plug them in at night.

How about a murphy bed? Pretty cool.

I loved the concept of a Murphy bed, until I had one.
it sat very low to the floor, which was fine for my tiny mother inlaw, but not so great for average height people.
I had to strip and store all the bedding to close the bed properly, and not damage the bedding. (Early on, I ruined a nice comforter leaving it on the bed...) I had to keep a tiny ceiling fan to allow the bed to raise and lower without hitting the fan. The bed had a drop down desk built in, which I used once to do a puzzle. Couldn't use it as a real desk because of distance from outlets.
overall, I hated the look of such big case goods in a small room. eventually, the bed just stayed down, but took more visual and virtual space than a normal queen did.
Any other chairs, etc, in the room had to be very light and moveable, or arranged so the bed could drop down without hitting something. I wound up giving away my desk, and replacing it with a small dresser for frequent guests.
If you don't want a full time bed in the room, I would look at something like the Ikea hemnes daybed that makes into a comfortable queen or king bed. it sits high, as a sofa, but makes a comfy guest bed, and more useful than a Murphy when not set as a bed.
Just my two cents.