I decided to do an opinion list off of every Pokemon of my favorite type (I don't think it's a big secret that Dark is my favorite type, considering how I've basically proclaimed that to be the case multiple times). I will count Alolan forms, but not mega-evolutions or Hoopa Unbound for this list (Grouping them with what they are megas of in the case the original form is still Dark type).

1. Alolan Ratata- Don't really care for it. (Neutral)
2. Alolan Raticate- I didn't like the original form, this thing looks really, really ugly in comparison to the original. I think somebody needs a refund on their root canal. (Dislike)
3. Alolan Meowth- Better than the original, but not much. Don't really care for either that much. (Neutral)
4. Alolan Persian- Why does this exist? Regular Persian looks MUCH better than this ugly thing. IT'S HEAD IS SHAPED LIKE A F***ING WATERMELON! (Hate)
5. Umbreon- Best Eeveelution, not only because it's Dark Type, or because it's unique among that type as a pretty solid support Pokemon, but also because the design is amazing. (Love)
6. Murkrow- I like this pokemon to some degree, because of the design and there's even some humor in gen 2 involving it. (Like)
7. Sneasel- Shiny looks weird (if the feathered parts stayed red I'd really love it though), but otherwise, kind of like it. (Like)
8. Houndour- I kind of like the design, though I never really use it that much in playthroughs. (Like)
9. Houndoom- Fantastic design, although the stats leave something to be desired. The Mega is a fantastic special attacker though. (Like)
10. Tyranitar- I may not really like Rock types much at all, but this godzilla of a pokemon is an exception to that, and a big one at that. (Love)
11. Poochyena- I'll just say meh. (Neutral)
12. Mightyena- I don't really like this pokemon. I don't necessarily hate it, but I definitely don't like it. Stats are bad, and the design is really meh. (Neutral)
13. Nuzleaf- I'm just going to say it. It looks funny, and ugly at the same time... (Dislike)
14. Shiftry- I kind of like the design, and it's quite original to say the least. But it just doesn't do it for me. (Neutral)
15. Sableye- I absolutely love this pokemon. Not just because of the design, but also because it had no weaknesses until gen 6, and their PMD2 appearances. Mega's great too. (Love)
16. Carvanha- I get it. It's a piranha... Design is original and so is the name, but I don't really like it to be honest. (Neutral)
17. Sharpedo- Interesting design, that sort of works for me. Also the mega looks bad@$$. (Like)
18. Cacturne-Another pretty meh one for me. (Neutral)
19. Crawdaunt- This pokemon is absolutely amazing. I love the design, and it's a really good physical sweeper, even if it is on the slow side. (Favorite)
20. Absol- I really don't like the original form, outside of a couple of the pokedex entries... But I like the mega, so I don't exactly hate this mon. (Neutral)
21. Honchkrow- Absolute bad@$$. Also, this pimp crow hits like a TRUCK with a crit moveset and Super Luck. Also my favorite Flying Type. (Favorite)
22. Stunky- Absolutely, very ugly. It just stinks pun intended. (Dislike)
23. Skuntank- Absolute @$$hole in PMD2, design is better than the basic version but I still don't really like it. (Neutral)
24. Spiritomb- Cool Pokemon, and probably one of the most original to date. Design is absolutely amazing as well. (Love)
25. Drapion- The design irks me slightly, but looks cool. Not entirely against using it to be honest. (Like)
26. Weavile- A huge improvement on Sneasel's already great design. And the stats are so great, it doesn't even need a mega to be great competitively. (Love)
27. Darkrai- Not my favorite legendary, but I absolutely love the concept and design of it and its power is frankly utterly absurd. (Love)
28. Purrloin- It may be absolutely adorable, but I'd be caught dead using one of these on my team. It's so awful stat wise unfortunately. (Like)
29. Liepard- Now this is how you do a cat version of Mightyena. Stats still are a bit lackluster, but it's OK. (Like)
30. Sandile- Cute Croc?  I also name every female mon I get from this line "Bea" or "Beatrice" in reference to the Night in the Woods character. (Love)
31. Krokorok- Cool Croc.  Also, when I get a Totodile, I always name it Krokorok simply because this evolutionary line is superior in every way. (Love)
32. Krookodile- My favorite Dark Type and one of my absolute favorite pokemon ever. I absolutely love sweeping with this thing.(Favorite)
33. Scraggy- Design could use improvement, and I wish it evolved sooner. (Neutral)
34. Scrafty- When Scrafty evolves (at level 39...) it's somewhat worth it just to see this design. If only this mon were better competitively. Still really like it. (Love)
35. Zorua- Interesting design, and I think it looks kind of cute at this point. (Like)
36. Zoroark- Yet again, interesting design, but I don't entirely like the appearance of the evolved form. (Neutral)
37. Pawniard- I don't know how they could possibly make a basic with this concept not look just off to me in a way I can't really explain. (Neutral)
38. Bisharp- Defiant is a very powerful ability against defog, and it has a really cool design. (Love)
39. Vullaby- Kind of ugly and really annoying to be honest, to battle in the wild and to evolve both. (Dislike)
40. Mandibuzz- Much better design than its pre-evolution. Pokedex entries are bland AF though. (Neutral)
41. Deino- 10/10 Creative name, Nintendo.  Also take all of my meh on this one. (Neutral)
42. Zweilous- Naming based off of German numbers? I don't know whether I should find that interesting or uninspired. (Neutral)
43. Hydreigon- Much better than both of its meh pre-evolutons. It honestly is a little dope. (Like)
44. Greninja- Most overrated starter pokemon known to man and thanks to how popular it is, I moderately dislike it actually. (Dislike)
45. Pangoro- Inferior Fighting and Dark type detected. I honestly find it really uncreative. (Dislike)
46. Inkay- Okay. It is a thing that exists I guess. (Neutral)
47. Malamar- Is it just me or does it look like it probably rapes people with its tentacles? Also take my meh. (Neutral)
48. Yveltal- Cool pokemon, weird name. (Like)
49. Incineroar- I can't lie, I like this cat, especially since Smash Ultimate came out. (Like)
50. Guzzlord- Probably my favorite pokemon from Gen 7. He looks absolutely awesome. (Love)   

(Favorite)- 3/50

(Love)- 11/50 

(Like)- 12/50

(Neutral)- 17/50

(Dislike)- 6/50

(Hate)- 1/50

(Despise)- 0/50

Aside from a few bad representations of this type, I generally at the least like most pokemon of this type, and the only mon I hate here is the absolute worst Alolan variant that was made to exist. There are quite a few I'm neutral on, but I feel like this would really be the case for any type, even my favorite of the 18 types. I might do more of these in the future and get an overall assessment of what my favorite types are, but I don't know. This was pretty time consuming as it is. I can't imagine how long it would take to do Water type anyways... A solid few hours I'd imagine...