That one looks really impressive! I'm definitely going to have to give it a shot. I personally haven't chosen one that I like best (although this one looks like it might be it) but I've heard a lot of good things about Handbrake.
HandBrake It has A LOT of options (I'm not sure about what file types it supports. but I know it's extensive and the info is bound to be on that site somewhere) The only reason I don't use is because I don't like to have to edit a lot of options. I just like a converter that lets me choose a kind of Low-Good-Best quality option and then starts converting. But that's because I prefer to have the lowest possible filesize while still having a watchable video. No HD for me
So If you're interested in really tweaking every setting of your video conversion, I recommend you try Handbrake, especially since it's free.
Also, video converting speed is reliant mostly on your computer specs, not the program. Most programs will convert as fast as your processor will let it. Changing programs isn't likely to significantly improve conversion speed.
As for video editing programs, there are a ton that are excellent, but most cost money if you want a good one. Power Director by Cyberlink seems to be a pretty good one, but it's really high end and costs a lot. A lot of people recommend VirtualDub (free) but I wasn't able to get a decent-sized video out of it (it went from like 700MB to over 4GB) and i just gave up on it. But that could have easily been a mistake on my part, you should try it out yourself. I think it has good editing options, but I didn't like the output file.
I think RealPlayer has some basic editing features, and I know it supports flv files. If you're just wanting something simple and don't feel like doing a lot of research or learning the program, just go with that one.
PC Media Manager: Get RealPlayer Free | Real.com
I have yet to find a good free video editing program I really like, so I'll be looking at other people's suggestions on this thread too. I use Audacity for audio (and it is amazing!) but I want a similar program that will also handle videos, and haven't been able to find one yet.
Note:I don't know how many of these support flv format, but if they don't natively you may be able to find codecs for them.
So those are all my suggestions and opinions about every type of conversion software I've used and heard about haha. Hope some part of it was helpful.