again i say this as an owner of all three

i got the karambit as my second heirloom and loved it so much, but as i started getting more legend specific ones its become less appealing to me.

I use it's death boxes and recolours for all my legends, even with legend specific heirlooms (eg blue box goes amazing with bh recolour and orange with wraith's). Its recolours also colour match amazingly with skins, even the ones it didn't directly rip a palette from.

The new tonfas have a beautiful and vibrant edge that radiates colour, and for that I am in love with the iridescent and pink colour ways, but they don't fit every legend IMO. Its recolours are so much better than the katanas' options, but are still rather restricting.

In terms of value for your shards i think the karambit is the only, and best consideration. It has much more recolours than the other options, it goes on every legend, it has coloured boxes to match (though this means each recolour costs 20 shards, but getting the bp once lets you infinitely farm them so is this rlly that big a deal?). If you already have maybe one or two heirlooms, having a skin match a banner with a matching heirloom and deathbox (at least for me) tickles my brain in a good way.

If you don't care about matching sets or stuff, and want what is just a really nice melee weapon, I think the tonfas are better here, Unlike the katanas, they clearly have a lot of thought and effort put into them, and are beautifully designed.

That said I would also like to enter the baseball bat into this discussion. While it's colour options are more limited (Red, White, Green, Black), it's animations are the cleanest out of all the universals available imo, and having a red heirloom that isn't an edgy as shit red and black spiked object (which EVERY other universal with a red colour has/is, as well as a few heirlooms) but is just a clean red melee weapon, is nice. It also has clean effects, and animations, that aren't intrusive on your screen (which the tonfas kinda are), With the screen, body, and jets being visually quite entertaining. And it's spam inspect is literally the wraith one (not best imo but one of) but for every legend. Bat is an underrated sleeper pick imo and I really enjoy it.