I don't even like Tanev, however his numbers are comparable to Pesce except his Quality of Competition is much harder. When you consider asking price it makes much more sense to acquire Tanev than Pesce. With that said neither make sense at all because they both get absolutely destroyed in the roles they're playing. Similar to Zaitsev on the Leafs. You're basically paying a premium to get a slight upgrade on the D-Man everyone hates the most on this team.
Lets move on...
On Anaheim, Hampus Lindholm is a stud. Everyone knows that. Josh Manson is also a solid player. He plays the same "shutdown" role as Tanev, Pesce, and Zaitsev. The difference is he's above average on his team in his role. I think it's fair to say his price would also be higher than the other 2 players listed above. Would acquiring Manson help the Leafs? Yes. The only question is if the value is worth it taking into consideration his age, contract, injury history etc. Manson doesn't have the complete game to be considered a top pairing D-Man, however he slots in as an above average shutdown guy in this league.
St. Louis is said to be a losing streak away from trading some core players. Pietrangelo, and Parayko are both top pairing D-Men comparable to Hampus Lindholm from the Ducks. Both have very good underlying numbers, and similar roles. Parayko has slightly higher Quality of Comp compared to Pietrangelo who has a slightly higher D-Zone Deployment %. I'd say it's a wash. The main difference is their age. For Parayko you're paying a lot more because of that as well as his contract. If you can get either player, you're acquiring a #2 RHD, the Leafs desperately need.
The last, and my favourite is Aaron Ekblad. After a ton of injury trouble, Ekblad has cemented himself as a bonafide #1 D in the league. Over the past couple years Ekblad has gotten slack for not developing the way people thought he would. Although I was calling for an Ekblad trade early in the year, when his value was at his absolute lowest, it may be too late now. Ekblad is playing some of, if not the hardest competition in the league, and absolutely excelling while logging massive minutes. He is also very young, and signed to a fair 7.5, that I'd like to call favourable at this point, and likely a steal within 1-2 years. Not to mention he has a point shots that the Leafs have been dying for since McCabe left over a decade ago. If you could design a #1 RHD in a lab that would compliment the Leafs to a tee, he wouldn't be as good as Aaron Ekblad.
In conclusion, I'll rank the players listed above in terms of best fit for the team. That includes age, contract, trade value etc.
---------- #1 RHD - Ideal
Ekblad - Absolute best fit for Leafs. No questions. If the asking price is reasonable you do it right away.
---------- Top Pairing D - Good Fits
Lindholm - Mainly a comparable, not on the block. Any team would kill to have him.
Pietrangelo - Better than Parayko. Age fits well, but isn't ideal. On ice play would help the Leafs immensely. Next contract though.
Parayko - Very good fit for Leafs. Asking price will be high. Would personally rather spend more for Ekblad.
Slavin - Same as Lindholm. Parayko and Slavin are close to interchangeable on this list. RHD more valuable to Leafs.
---------- #3 RHD - Decent Fit
Manson - Good fit. 27 . Above average shutdown RHD. Not a ton of offensive upside. Serves his role.
---------- #4 RHD - Wouldn't trade for unless price is below market value.
Pesce - Asking price is insane (Kappy), not a bad player. But shouldn't be playing top comp on a cup contending team. Solid 2nd pairing guy as long as it's not in a matchup role. Bad possession player, that would already hurt a bad possession team in the Leafs.
---------- Bottom Pairing RHD - No.
Tanev - High Quality of Comp, bad results. Injury prone. Better than Zaitsev, but not good either.