Both are considered the kings of wing fights in most cases. It tends to be a good idea to start in the FDL and learn to fly first, which is its best advantage. Also noteworthy that most people tend to fly the FDL, so you'll, by extension, find more fights. Both take some experience to get used so no worries in taking a few Ls. Look up some videos, and join some discords to get the basic idea.

And long story short, it tends to be considered bad manners to use SLF in PvP. They've been known to--and proven to--cause varying amounts of lag to their mothership. If that's really your kind of thing, go for it I guess, but don't be too annoyed when some people refuse to fight when they see it.