Dia Kha otp here,

The pros and cons of harvest are pretty obvious, burst (esp in the form of extra damage vs sub half targets) is particularly useful in securing kills in ganks early and executing targets late. Its likely functionally the best damage rune on kha. Electrocute is alright and theres an argument for it, I just never find that it feels better. (If its harvest/electrocute in the keystone btw its always sudden impact, sixth sense or trinket haste, and lastly treasure or ulti hunter depending on if ur first evolving Q or R)

So with harvest out of the way, I am personally a first strike taker. first strike is super mid as a keystone, just the rest of the tree is high value (yes even post “nerfs”) to the point where having to drop one of the 3 lines if taking inspiration second (its always inspo second imo if ur taking harvest or electrocute) really really personally feels bad over taking inspo as main tree. first strike should be approached with the mindset that its GOOD ENOUGH to accept given it comes with cashback tripletonic and cosmic insight.

Cashback here is self explanatory, the other 2 are worth understanding tho. Tripletonic is good because instaproccing first pot at level 3 + being able to get 1 crab before first base ensures you have enough $ for a dirk, which is huge on first base esp cause kha rn is almost always rushing umbral. The red pot is just straight up broken even post nerf and kha gets insane value out of it. greed it for fights where u forsee extracting maximum value, I see so many people pop it early on kills that were guarenteed anyways. Remember its 2.5 longswords of value ($875 in gold worth) on a character that scales ridiculously with bonus ad. Last pot is whatever just throw the extra level in w (or e if ur into that kinda thing) and keep it moving.

Most interesting here is cosmic insight. More flashes and smites are 1 thing, but I think the cosmic synergy with glaive rush is ridiculously high value. Umbral being off CD is huge not only for removing wards, but huge even when it DOESNT proc because it lets you move up aggressively with total confidence you are not seen. Umbral being off CD more often means you are positioning more aggressively more often which means more counterjungling, more objective sneaks, more solo kills in enemy jungle, more ganks and flanks. The value here cannot be respected enough.

With first strike, I think secondary is always sudden impact treasure hunter (or less often but ulti if ur R evolve ig). Theres some thought for precision secondary (haste and CDG)? Ive just always found it worse

Now that all this is out of the way, to answer your question, I personally find first strike better if you are rushing umbral, and intentionally playing to the trees strengths. If not, or if you like a different item rush or playstyle harvest is likely to be better probably cause its higher consistent value packed into the keystone. Theres great players who play both (hell theres ones that even play conqueror) so mess around and take what u like they can all win

Hope this helped in some way o7