I have a 22 gallon long tank, with a Oase Biomaster 250 filter which is pretty strong (designed for 50-70 gallon tanks).
I need to get a lily pipe that will give me surface agitation. Which one below is better, and considering that my tank is small with a very large filter?
Anything that creates bubbles is best. Lily, poppy, spraybar, "normal", "normal" with venturi (sucking air in); it's all good as they can be directed to brake the water surface in such a way that air gets sucked in, creating bubbles, by which the water surface is further disturbed.
Lily and poppy have a way of channeling the water, which makes great marketing material.
For a poppy to have optimal disturbance, you have to place it a little out of the water in order to suck air in. But this in turn affects the way water moves through your tank. It is hampered somewhat, so it would not have my preference.
There are difference routes to Rome. A poppy, lily, spraybar, gooseneck, or whatever, is one thing, the way one applies it is another. So poppy is not by definition better or worse. I think the people who purchase these outflows (as I did in the past) just thought it is cool how the water tuns inside a lily or poppy. And of course, a lot of gorgeous Aquascapes on the internet display them as well.
But I've tried them all. I prefer a spraybar myself as it can cover the entire width of the tank. If you add a venturi system to the spraybar, you can a lot of bubbles. You can also get these bubbles if you place the spraybar above the waterline.
But your question is lily versus poppy; the poppy is sometimes preferred, I believe, if the water flow coming out of your filter is very strong and you like to brake it somewhat (again a spraybar can do this also). Then again, you can reduce flow on most filters.
So look at some vids on the internet and decide which you prefer. For water disturbance, I don't think there is any difference. It depends on how you apply the lily or poppy.