I mostly use Assassin because I have an Infected skin from...what is it, 2-3 years ago now? Someone dropped it in the Nexus, so I quiccly picked it up and I still have it unlocked. But then I got a Mystery Skin, which contained an Agent skin...and...dyes just look so much better on it...
Anyway, I think it depends on how much you enjoy the class! Using a Harle is great for a newly rolled Assassin, since you'll definitely be able to throw two Baneserpents/Nightwings with it. Combine with a health/defense ring to keep up your survivability if you wish, or go full @Desotroya and wear an UBMP, then die in an Abyss because you had too little health and defense. (;
But for events, Assassin is pretty good, as his range is pretty much St. Abraham's pre-range nerf, and then some. Sure, with the invulnerability phases combined with semi-steamrolls, it can be tough to land a poison precisely (which is why we need that poison throw time decrease!), but for events that don't go invulnerable aaaaaaaall the time - such as the LotLL, Pentaract, and...other stuff...it's great!
also you have pretty decent DPS. Foul is safest, but a Spirit might work as well. Cronus/Etherite if you're absolutely sure you can go in deep. RIP my free Etherite I got from a Cemetery because I played unsafe :')