Sealed Falchion or Bond Falchion Refine?

Sealed Falchion definitely. Less strict of a requirement for greater bonuses.

I personally prefer the Bond Falchion since it gives Renewal 3, allowing for healing when in danger and Aether.

Of course, Sealed Falchion, I guess, would be better if you're planning on leaving Chrom to his own affairs while the rest of your team goes off somewhere else, I guess?

Sealed Falchion and Aether don't go well together IMO. And the HP threshold on Quick Riposte doesn't complement Sealed Falchion much either. I'd opt for the build you have now, as I really think Sealed Falchion's reduced HP trigger requirement encourages a player phase build.

It just depends if you're deathballing or not. If you plan on playing Chrom in a tight-packed team, where all the units are next to each other, use the original Falchion.

If you plan on playing Chrom as a rogue unit and have him go off to fight enemies alone, Sealed Falchion is far better. The stat boosts are definitely worth it, and it's easy enough to take a small amount of damage to trigger the ability.

Additionally, Sealed Falchion lets Chrom play on the Player Phase a little more if necessary, since he keeps his buffs in both phases. Falchion's effect refine is really only good for enemy phase since it's difficult to keep him adjacent to an ally when attacking otherwise.

I think chrom prefers the bond falchion, specially since you have built him as a baiter, so the bond will be a lot easier to use, and he really appreciates the healing.

It depends on what you're going for, Sealed Falchion is for aggressive play, since it loses it's built-in Renewal which means you won't be knocked out of skills like Brazen or Desperation prematurely. Bond Spectrum Falchion is for baiting and it does require a more expensive approach since you need Distant Counter to make use of every stat while also using Quick Riposte to ensure doubles.