We use both Zenefits and Gusto (mainly because of legacy issues - neither offered both benefits + payroll when we started)
Zenefits manages our health insurance and onboarding, and Gusto does payroll. We don't pay Zenefits directly. With this layoff, there's about zero chance I would consider switching to their payroll service (even though it's about 20% cheaper than Gusto)
Gusto has a really solid UI. However, their problems are that unlike ADP, they require a long lead time (5 days I think?) for payroll. They also don't differentiate between part time and full time staff which makes this prohibitive if you use a lot of part time staff with few hours. Neither service provides a "full stop" HR solution - we have to use WhenIWork for timesheets and scheduling, and Workable for an ATS. I could justify their pricing if this was all rolled in.
Gusto recently doubled their prices so we are looking at OnPay which is about 1/3rd the price of either Gusto or Zenefits for payroll.