I'm a huge fan of the strategy of rostering elite middle relievers/setup men for help in ERA, WHIP and K. I'm especially fond of this strategy in leagues with innings limits (because great middle relievers are very efficient on a per inning basis) or GS limits (because relief innings don't count against the GS limit). Some analysts even encourage rostering multiple of these guys to "create" an ace.
There are places on the internet that rank middle relievers for the purpose of potential saves down the road, and there are places that rank them for holds leagues, but I've never found any sites that rank them solely for their ERA/WHIP/K contributions. That changes today, with my top 10 middle relievers for ERA/WHIP/K list:
1. Dellin Betances
2. Andrew Miller
These two are just way ahead of the pack in this department. The only hard part about this is separating the two of them. If we were factoring in save potential and holds, Miller would get the nod as he's the clear handcuff to Chapman, but for solely ERA/WHIP/K the margin is razor thin. I anticipate similarly ridiculous ERAs, Miller to have the slightly better WHIP and Betances to have the slightly better K/9. The deciding factor was Betances' likely heavier workload. He's led the AL in bullpen innings two in a row, and that both mitigates Miller's likely WHIP advantage (since his will be more heavily weighted) and amplifies his K advantage, while also giving his ERA more weight.
3. Shawn Kelley
4. Kevin Siegrist
These two actually have identical K-BB% numbers (33.9), which, as you can imagine, made them exceptionally hard to differentiate. Typically, I'll lean towards the guy with the better K% - strikeouts are their own category, and a high K% can make walks less painful - but in this case I felt there were some other indicators pointing toward Kelley. His SwStr% is substantially higher, for one. Also, Siegrist is giving up too many flyballs for my taste - homers can really screw up these types of guys.
5. Michael Feliz
I really wanted to rank this guy higher, but I think I need to see a bit more longevity in his recent run before I move him up too high.
He gave up 10 runs (9 ER) in his first two big league outings this season, but has been unbelievably dominant since:
6 G, 11.2 IP, 0.77 ERA, -0.19 FIP, 14.66 K/9, 0.00 BB/9, 0.26 WHIP, 50.0 K%, 0.0 BB%, 17.9 SwStr%, average fastball velocity of 95.4.
His fastball velocity is also trending up:
(earliest) 91.5. 94.6, 93.6, 93.7, 95.6, 96.3, 96.9, 96.4 (most recent)
Over the last 30 days he's lead all RP in K% and is one of only six qualified RP to not issue a single walk.
The Astros are not hesitant to use him for multiple innings, so he could put up lots of innings to amplify the effect of those superb ratios (a la Betances).
6. Seung-hwan Oh
7. Nick Vincent
8. David Hernandez
9. Kelvin Herrerra
10. Hector Neris
Don't forget to follow Pitching Breakdowns in Twitter (@PitchBreakdowns)!