I'll step in as one who prefers Efke over FP4+, but both are fine films and although Efke works better for me I'd be unsurprised to find that FP4+ works better for others.
One thing I will point out is that it's unsurprising that your comparison of the two films is giving you Efke negatives that are significantly grainier. Rodinal 1:50 is generally recognized as providing negatives that are perceived as very grainy, whereas D-76 and clones thereof tend to clump the silver less, leading to less grainy looking negatives even at 1:1. Try developing some FP4+ in Rodinal and compare it to the Efke; I'm sure you'll find the difference much smaller. "Apples to apples...", as they say.
As to why I prefer Efke 100: I develop most of my film in Pyrocat-HD. My 8x10 negatives are all contact printed on Azo whereas my smaller negatives are all enlarged. I've found that I can build density forever with Efke. The film gives me the look that I want, with wonderful mid-tone separation, great shadow detail, and highlights that hold detail extremely well. I did try FP4+, but using my normal chemicals and procedures I found that I couldn't get the same amount of expansion or contraction out of it as I could with Efke 100. FP4+ is an excellent film, but using my procedures and for my purposes, Efke 100 is a better film.
The downsides to Efke are the obvious: it's extremely soft when wet and is easily scratched (I use a Unicolor drum and don't have any problems) and it really isn't an inexpensive film although some perceive it as such. J and C are the only distributors of note in the US, but I've found their customer service to be top notch and I'm happy to support them.
Regarding perceived shortcomings: I keep reading about emulsion defects with Efke film, but I've never found one in the film after having been through more rolls of 120 and boxes of 4x5 than I can remember, as well as a lot of 8x10. If there were defects, they were either too small to notice or of a type that didn't cause me any problems with my final prints. As to edge fogging: I've not seen it, but it's possible that the paper isn't as tight as that on other films. I make it a standard practice to use the black plastic tubes that J and C sell for all of my exposed 120 film and I've not had a light leak yet.
Using my processes and procedures, I find that Efke beats any other film I've tried for both expansion and contraction. I've run it at N+2 through N-4 with no problems, and I suspect that N-4 isn't near the end of what's possible with this film. Efke 100 responds wonderfully to stand development with Pyrocat-HD (and with very highly diluted Rodinal, for that matter). I've shot thousands of frames with Efke 100, and it remains my favorite film.
Again, I'm sure that FP4+ works better for some people...perhaps even most. But in my work I've found that Efke 100 is unbeatable, and personally I'd happily pay more for it than for any other film of comparable speed. It's possible that it's the use of a staining developer that gives Efke 100 the edge in my darkroom (although I have used Rodinal for stand development, and I believe Jay does a lot of work with staining developers)...if you want to try a staining developer then you can give Pyrocat-HD a try. In the bottles provided by Photographer's Formulary, it really is a "no fuss" developer that's as easy to use as almost anything else.
Be well.
Dave