Both! Given Void Summoner's existence, you can expect to get Shadowfiend to around 1 minute as Voidweaver or 90 seconds as Oracle and Mindbender to around 40-45 seconds. As a result, you will use both depending on which one fits the fight timers better. The most important thing is to make sure that whichever pet you run, you are getting as many uses of it as possible.