Lessee... your choices are either going to lean towards utility or having a shadow weapon.

Let's break it down, then. For utility, your choices would either be a status weapon, or a pulsar; you already have a shock weapon, so discounting the voltech alchemer, you probably want either the firotech or cryotech alchemers, or a pulsar. Cryotech alchemer and Pulsar are both good at keeping enemies at a distance when you don't want them near you, and the latter can be used to group enemies together as well. Firotech can cause high damage over time from a distance, but the initial damage is elemental, which means you'd rarely use it over your sword. Cryotech has this as well, but you'd be using it for the freeze effect, not the damage. Pulsar you have a choice of elemental damage and normal damage - which you choose is up to you.

For shadow damage, you have the Toxic Catalyzer line, or Shadowtech Alchemer. The former needs practice to use well, and a good team that knows how to avoid screwing you over. The latter is pretty simple to use.

So, again, your choices:

Cryotech Alchemer - Freezes enemies; not necessarily better against anything you can use your sword against. Alchemers have a very high growth in damage from their charge attack as you upgrade them.

Pulsar - Amazing crowd control, you can choose between useable on anything (Supernova Line) or very useable on anything you can use your sword against (Polaris Line). Range and blast radius both improve as you upgrade it.

Toxic Catalyzer - Amazing damage to monsters you don't already have a strong weapon against, needs you to learn how to use it and a good team. I wouldn't know for certain, but I'd expect the blast radius improves as it upgrades. Poisons enemies, too - very useful at JK, and helps your team slightly anywhere.

Shadowtech Alchemer - Covers the third damage type, simple to use. Again, Alchemers have a very high growth in damage from their charge attack as you upgrade them. The shadowtech alchemer doesn't offer much in the way of utility, though.