What's the best thing to use for Marror (bitter herbs) for Seder, taking into account Halacha, ease, availability, etc?
Well, here are the pros and cons as I see them:
Iceberg lettuce: PROS: It's easy to find at any supermarket and cheap. As far as bugs go, take off the 3 outermost leaves, quarter it, rinse it, and you're done. No bug-checking required. (The bug-checking thing can be heard from Rabbi Genack here.) It's said that R' Yaakov Kaminetsky's usual Marror was iceberg lettuce. Rabbi Moshe Heinemann also opines that iceberg can be used as marror. CONS: Many people, especially in Israel, don't think it's real marror (not bitter enough!), or only use it if there's no other option.
Romaine lettuce: PROS: good availability; I think everyone accepts that it counts as marror. CONS: must be checked for bugs. Unless you can buy the pre-checked stuff, which can be expensive and/or hard to find. I called a produce wholesaler who said Dole told them they had kosher-certified plain chopped romaine, but then later Dole said sorry they didn't.
Horseradish: PROS: no bugs. Not too hard to find. Had traditionally been used by Eastern European Jews. CONS: A painful (hot, not bitter) experience. Unclear at best if this was among the species described by the Talmud (all the others are in the composite lettuce family, have milky sap, etc.). As one rabbi said: "I use romaine for real, and then a little bit of horseradish for tradition's sake."
Endive: PROS: listed in the Mishna (see Tiferes Yisrael's commentary). Tasty. Not very buggy. Available from any good produce supplier. CONS: I've never seen anyone use it. Expensive. Small, so you'll need a lot of them.
Dandelion: PROS: also in the Mishna (look up "charchavinim"), and in the lettuce family. Tastes bitter. CONS: where can you find lots of them? Do the ones in your yard have pesticide on them? Dandelions are a very strong diuretic, so make sure your system can handle them first.
The other plants mentioned in the Talmud (chicory anyone?) generally aren't used today as far as I know; not sure how certain we are of the translations. And it would look weird.
It seems clear from Pesachim 39a that Chazeres (lettuce) is preffered for Maror. Several reasons are given.
Rav Acha the son of Rava reversed himself and admitted to Ravina that lettuce was better even though it is not as bitter.