What is the best weapon

Binding blade gets my vote. Dragon effectiveness, QR5, 16 might, 4/4 defenses when attacked is a bit loaded for a weapon. Though there are a few that contest it.

IMO, it's any Falchion. The variety of stat bonuses and effects makes the user more versatile and flexible.
For example, the Bond/Sealed Falchion users can be dragon-slayers, combat medics, defensive tanks, offensive sweepers, etc. given the right build.

Interesting Question. I dont know much about Aesthetics, since I dont pay much attention to them. I can do gameplay.

The obvious choices are Dire thunder, Celica's Ragnarok(refined), Mastersword, Thunder/berserk Armads, Thani type weapons(Eg: Wingsword), Forseti, Great Flame, Ayras blade.

Those aside, a few mentions should be given to bladetome/Thunderhead and owl weapons, as they are devastating in the correct team comp. Firesweep weapons should also be recognized, as being bale to poke enemies without retalitation is a very good effect. Other good but not outstanding weapons are Veronicas staff(I wont even try to spell it), Flora's dagger(Lol fuck DC), Felicia's plate, Divine Tyrfing+ many more.

Ares's Dark Mystletainn get a feature here because of how underrated the weapon is. Ares is the only unit capable of endless looping AOE specials after the first activation. (-1 from attack, -2 from after battle, with slaying edge effect), which makes him a monster capable of killing more high defense blues(since AOE's ignore WTA).

I care mostly about the looks and in that department, I'd probably choose Wolf Berg from prf weapons and Kadomatsu as an inheritable weapon. Wolf Berg just looks evil, which is a plus and Kadomatsu is the only nice looking inheritable sword.

I guess, that if I was forced to choose something based on its ability, it would probably be something like Exalted Falchion, because of the buff interaction or Niddhog thanks to being the only bow that's actually interesting to use.

If we're talking melee weapons;

Urvan looks great, it's a big axe with both a simple but a regal design. Maybe a bit oversized, but it's fine.
Ragnell and Alondite are pretty cool too, love that they're counterparts.

Raijinto is pretty good too, a fine balance between fantasy and realism. It's slightly too ornate but it still looks like a weapon someone would use. And the lightning is just cool.

As for effect
All versions of Falchion, Armads and Siegmund.

Edit:
I should mention Mystletainn for both aestetic and gameplay.
It just looks beautiful, I'd say. And again, my personal taste is when weapons strike a balance between beauty and if it's practical
Mystletainn has a nice size, good guard ect.

For effect, the fury is simple but effective, it allows for some fun builds.
The special spiral effect is scary and allows for some fun stuff with AoE specials.

Thani because seeing the ball of light animation was always funny to me ever since I started playing the series with RD. Plus the effective damage while also hitting res is incredibly nice. And I mean Micaiah's just great, she might have even had a chance of being my favorite RD character if Mia didn't hail from Tellius as well.

Other good ones are Valflame and Forsetti, again those animations were also very fun to see in Genealogy. And for physical weapons Resolute Blade, Dark Mystletainn, Gae Bolg, and Hauteclere.

I Think One Of The Best Weapon Is The Breath Of Blight. Heal You While Doing Damage To Enemies And Breath Of Fog And Falchions Aren't Useful. I Think Skadi Is On The Run For Me,With Yato And Divine Tyrfing.