Here is what you should be looking for:
Reliability: they need to know what they’re doing. Favor providers with proven experience validating on the network.
Communication: you’ll need to get information and support from them, on a regular basis. Be sure to pick a team that speaks a language you are comfortable with and matches your availability.
Economics: go for a competitive fee. While in theory “the lower, the better”, avoid 0% fees - validating on the network is not easy, nor cheap.
You can find a list of the Staking Providers here: https://explorer.multiversx.com/providers or you can select one of the providers featured in the app.