In a roto league, where it didn't matter when each pitcher contributed, if I didn't need a lot of innings from my waiver wire claim, I'd go with Hernandez.
I wouldn't plan on more than 100 innings from Hernandez. But Williams and Westbrook don't strike anyone out. I'd also look for both to post an ERA near 4.00. Hernandez at 100 innings will give you 4/5 the strikeouts that either Westbrook or Williams will in 200 with much better rate statistics. If he reaches 150 innings, he'll give more strike-outs using up fewer of your innings (which may be good or bad, depending on the rest of your squad).