Binder is probably still the best for aether damage and is also the most versatile aether class I would say. Spellbinder works great with melee, caster, or hybrid aether builds, so you can easily respect later when you find out which playstyle you prefer.
However, leveling as aether is a little bit tricky, especially for melee aether. Most aether spells are energy-hungry (CT, AAR, DE), so leveling only becomes smooth around lvl 20-30 when you have enough energy regen. CT and AAR also need gear to convert fire, lightning, or elemental damage to aether. There are three aether leveling guides in the forum: Stupid_Dragon’s CT + Devastation Spellbinder ([Caster] Beginner's Nephrite Spellbinder), Ulvar1’s DE Apostate ([1.1.8.1] Uroboruuk - a build journal and guide for SSF Drain Essence Apostate), and Nery’s Lucius Battlemage ([1.1.8.1] Beginner's 2H melee Lucius Battlemage). Ulvar1’s DE does not involve arcanist, but you can probably do a similar build with binder. DE leveling is quite hipster though and pretty slow until you get some MIs that help its AOE.
Since you already are an arcanist, I would go for either caster Spellbinder with AAR, CT, or Devastation (you should probably combine devastation with AAR or CT for smooth levelling) or melee Battlemage like Nery’s guide. Melee Spellbinder is also great for endgame, but levelling with it is tricky since neither Arcanist or Necromancer have spammable melee skills. You would need either shard of beronath (only available at level 55 and only if you have the blueprint) or Heart of Theodin Marcell mace, which provides Fleshwarped Strikes, but is only available in act 6 and requires you to target farm decent ones from the final boss (could be annoying, especially if you plan to dual wield). Aether AAR has no levelling guide, but it should be easy as long as you can manage its energy cost and get some AAR MIs while levelling (select to show only rares on this link https://www.grimtools.com/db/search?query=aether%20ray&in_description=1&exact_match=0). For off-hand, I would go for Pulsing Shard because of its life steal mod, but Fleshward Tome provides more damage, especially if you are maxing Disintegration.
CT is considered casting, even though it is a low range spell.
The level 30 version of Soulsplitter? It would be tricky to level with it since aether melee is not great at this level range, but you could try. It would have to be Battlemage with soldier melee skills though (probably blade arc). For you to have an idea, some very basic aether blade arc skill allocation would require you to be level 43 (something like this https://www.grimtools.com/calc/0V0mpYRZ). At that point, Lucius weapon would be a better 2hander than Soulsplitter. For casters, the MI offhands are too good to use Soulsplitter and its attack speed roll would be useless (it is designed to be an attack weapon).