I'm sorry but I just can't recommend a Fenix LD10 over a Nitecore D10 at this time.
I have both sitting side by side as I write this and there is no comparision.
I hit the piston on my brand new Nitecore D10 Tribute and it came on. No flickering at all on any level. I was able to switch from the lowest mode up to the highest in about a second. It worked as advertised and expected.
I then turned on my brand new Fenix LD10 R4. The low mode came on with no problems at all. I waited a second or two and then went to the next higher mode. The light started flickering right away.
It continued to flicker when I went to the highest mode (non turbo).
When I tried this again, both lights worked as designed with neither flickering. The Fenix didn't show the problem for several dozen activations but there is NO WAY I would trust it to perform correctly when I really need it. The Fenix L1D I have has the same problem as the LD10. In fact, it (L1D) has actually messed up twice when I used it in public to assist someone. I had to put it on Turbo mode for it to be stable. It really proved untrustworthy at that point and I purchased the D10 and later the LD10 because of it. I hoped the LD10 would prove more reliable but it has actually been worse (since the L1D didn't start have this problem for almost a year).
I'm no Nitecore fanboy (I only own one at this time) but it has proven to be far more reliable at this point.
This isn't a cost or price issue. I've got half a dozen Surefires that I love (E1 Outdoorsman x2, E2DL, G2, 6P, etc) and the only reason I don't usually EDC them is the battery type. I prefer using an 1xAA light for EDC use since I never feel that I'll have a problem using it too much and not be able to find another battery (I've never seen a CR123 at a gas station quicky mart).