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But typically I advise to paint poplar- its grain is excellent for paint, not so good for stain. At same time, if this is new construction, can you ask to have a mockup done in stain? It should be a large piece and placed in the room near the actual trim location. It should not be a problem for the painter to do it. Good luck!

The good thing is you can buy a piece of poplar the size and width you need from the big box store. Stain it a few stains you like and put it next to it. Poplar is normally painted because it is tough and smooth and take paint well. It has little grain, no knots but can have dark areas. So do a test, ask your friends and decide.

Ah, pics loaded, nice space! I stand by my comment above and agree w/ fredm51. Also, if you see the baseboard in the pic with the dark parabola shaped grain, that color difference is common with poplar. Some folks love to accentuate that contrast, others hide it with paint. Do some tests and decide.

Thank you both, that all makes great sense and will definitely do some testing.

I say paint it. You will never regret painting it as it will feel so fresh and really stand out against darker colours on the walls should you wish to go that route. And with your floors and kitchen cabinets wood, you may find it is too much wood. Also, your floors are really beautiful and I would love for them to stand out.

I say stain it- painted trim gets so dirty! I had wood stained trim at my old house and thought I would prefer painted- totatally regret that decision!

If it were an oak or something with nice grain I might opt to stain. But poplar is blah and so I'd paint it. Those corners will pop beautifully with paint!

Looking good so far. I think whether you stain or paint depends on what direction you are going with decor. If you are leaning towards craftsman style, earth tones, & wood blinds, darker furniture the stained may look better. If you are leaning towards a more updated style, grays, pottery barn style, white would look better.
Others may think different but that is how I see it. Try to visualize overall finished look you want. Personally I like the white especially with the nice wide baseboard you have.

I'm seeing some nice grain in that poplar and I would just stain it but I do love wood trim. Look at it this way, you can always paint over stain but once painted that's it. Also stain quality trim is much more expensive than paint quality so why pay more for clear wood and then paint over it?

Paint it and don't look back;)

I don't think poplar usually takes stain very well. I've always thought of it as a "paint grade" wood. I would paint it (and that is coming from someone that lives in a house with stained trim)

Don’t stain poplar. You won’t be happy with the results; the stain will look blotchy. It is a good wood, although soft, and inexpensive and takes paint very well. You are not to be worried about painting this wood...it is common. Nothing special. Were the trim walnut or oak, then you would have a conundrum.

Looking at this beautiful space, I would advise painting the window trim and baseboards and as @Margo C. advises, don't look back. The reason: having all that trim as contrasting elements is visual clutter. It makes the interior look kind of cartoonish. Paint the trim the same color or a close value (brightness) to the wall but use at least semi-gloss. The gloss makes the trim stand out finish wise, without adding 'noise' to the interior. That way, the wood grain in the millwork and the hardwood floors can take center stage and you will not have too much of a good thing.

Please listen to those above advising you to paint rather than stain poplar, as it isn't a wood usually recommended for a stained finish. So the question really shouldn't be whether a stained or a painted finish would look nicer in your condo, but whether the wood species that has already been installed is appropriate for both options:

http://woodworking.about.com/od/typesofwood/p/Poplar.htm

I sugested to do a test, this would let owner say I tried that and never look back. But to remove the paint so stain could be put on is crazy. The sapwood can look green in spots with a light stain. This is why I never offer a paint color in discussions.

I'm really grateful for all the thoughtful responses and expertise. I will certainly see how the test staining comes out because why not, but seems like paint might be the way to go. Will be sure to post 'after' shots whatever the outcome in a few weeks time.