I can't really make any good puns with Ghost-types, since they don't have the life of some other types, but whatever.
I don't know what the hell got into me, forgetting that Cofagrigus was my favorite Ghost-type; I love the hell out of this thing, unequivocally - it's a very solid defensive wall, has a lot going for it being able to neutralize the ability of physical attackers, it can be a nice little addition to the team in case you're missing any kinds of walls, and so far the only rival it has in that department is Runerigus, its Galarian counterpart. But my favorite part of Cofagrigus is its concept and design; Yamask, its prevolution, starts off carrying the mask of the face it used to wear as a human - then that mask becomes an ornament on the sarcophagus part of Cofagrigus. Its color scheme is really cool, too and goes along great with an Ultra Ball, imo.
Also, as long as I'm talking about Cofagrigus, as I was searching up Cofagrigus's artwork, I found some really cool pics without meaning to; whoever made these, good job. These are great.
- Gengar: Meant to put this as just a mention but I forgot my real favorite Ghost-type until Fuzzy reminded me with his comment. I feel like a dumbass.
- Cursola: An evolution to the Ghost-type Galarian Corsola, Cursola is just the thing Corsola needed - especially since Gen 7 gave it a natural predator in Toxapex; Cursola is just the love this thing needed since it's not really that good, otherwise, not mentioning that it also has access to a bunch of good moves, including Strength Sap, which cements Cursola's place as a tank like no other. I haven't gotten to use it, though.
- Dragapult: It's a great pseudolegend and the Dragon/Ghost-type is something that needed to be distributed more beyond just Giratina; it's got a great concept in being based on an extinct amphibian and a stealth bomber. But personally, I still feel like it's missing something, honestly. Maybe in Gen 8's enhanced version, it'll get a Gigantamax form? Who knows? I hope it does.
- Dusknoir: Really solid design and use, but has the nasty problem of being both a Trade Evolution and a held item Evolution; if GF ever adds a way to circumvent it, maybe it'll be my favorite some day. Until then, don't fear the reaper.
I'll be honest, I don't really have a least favorite; this is one of those types that I don't really have many that actively annoy or frustrate me, or visually repulse me either. It's a weird situation. There are a few that mildly bug me, though. Mainly the Kalosian Ghost/Grass-types in Phantump/Trevenant and Pumpkaboo/Gourgeist - why are they trade evolutions? They don't need to be!