I like rhodiola, mostly because it gives me a small stimulant type effect, without producing anxiety. I've taken a few different brands, but the most effective brand so far, has been GAIA herbs, only problem is its expensive.
I usually take mine in the morning and it lasts for about 4-5 hours i think, but its really hard to tell. I think its a great mixer, as in it mixes great with other drugs like pot, alcohol, ativan, etc. To me, it has the effect of bringing a brightness to my day, it has a pretty good effect on uplifting mood when my mood is neutral to begin with, not when I'm in the depth of depression, but it can help me get out of that too.
And I think the effects Do change over time, the more you take it, the more effective it is, there may be a tolerance issue, but I think it works like an ssri, you gotta let it build up in your system and then reap the benefits, but I think its also important to take a break from it everyonce in a while to keep your system guessing.
And not that this has anything to do with rhodiola, but ginseng is also a very effective herbal supplement. It energizes it a good libido booster, it even helps me concentrate sometimes, the only problem is is that it can cause me to be pretty anxious and jittery, which is why I like taking it with booze or ativan