I hadn't actually read any Verne since I was much, much younger, and I'd recently decided to get some. Somewhere online I stumbled across some more information on this. A quick search on Google for Verne translations or anything similar should give you plenty of info, but here's the basics as I've uncovered them:
Anything in the public domain probably sucks. There were basically no good translations of Verne to English when it was originally published and nobody bothered to fix that for a long time.
I was specifically looking into Twenty-Thousand Leagues, as I'm sure many others here will be. Mercier Lewis (or Lewis Mercier) is apparently the primary translation and one of the worst. Barnes & Noble has a line of classics republished in trade paperback for cheap these days, and I've been enjoying them, but their 20k is the Mercier version. He drops huge passages, especially all the science and socialism, and in many cases screws up the meaning entirely.
In the 1980s or so, a gentleman by the name of Miller produced a new translation that is supposedly much, much better. I think he may have also done a couple of Verne's other books, but not many yet.
Since translations are covered as copyrighted works, the new versions will tend to be much more expensive than the old public domain versions. My county library has a copy of the new one, and I just put in an ILL order for it. If you don't want to spend the money, everything I've uncovered says you should do the same instead of waste a few dollars on an old and misleadingly poor version.
Edited to add: Ok, I'd only glanced at the linked article before posting this, and now I've read it in detail. We seem to agree on a lot, and he has more experience than me. As far as I can tell, the Miller version I discovered was published in 1993. He had a much earlier version that was a reconstruction of Mercier, but finally started from scratch and also annotated it. Butcher's version (which the linked article mentions) is from 1998. I obviously haven't read them to compare, but apparently people in the know think that both of these are accurate representations of Verne's original work.