OneSignal’s omnichannel customer engagement platform offers push notifications, email, in-app messages, and SMS. OneSignal’s automated customer Journeys and one-off campaigns allow users to create messaging strategies that convert, inform, and retain audiences, with little to no coding required for setup.
I think One Signal is very well suited for mobile app owners who want to be in touch with their user base more easily by sending push notifications and in-app messages. I'm not sure how well that works for SMS messaging as I haven't yet tried it. I wouldn't necessarily recommend it if your in-apps are very rare.
If you're looking for mobile segmentation, CRM, multivariate testing, then Swrve is the way to go. It's not a great analytics platform, but it's improving on that front.
I give an 8 in this question mainly for 2 reasons: the products even if they look like complete and are highly customizable and usable, they are still missing some logical features. For example, send messages to a list of users - now days you can do it with postman and get calls. A second example is App messaging that is still in development and has many opportunities.
Their customer support has been top-notch. They are able to assist you in getting through any problems that you may have and respond in a very timely manner. I've dealt with them on 4-5 instances over the years and my issues were always resolved within a matter of a few business days.
Look Firebase is a complete platform that includes a Push notification/InApp space. We had a lot of troubles while implementing Firebase: sometimes we thought it was ready until we tried to attach an image for Push notifications. This being said, the developers had to review the integration several times until we decided to change to OneSignal. Also while using Firebase I was not convinced with the look and feel of the Notifications. My vote here is OneSignal.
Localytics' Analytics interface was more simple to use, but we chose Swrve primarily for the messaging capabilities and the analytics were a bonus. We found Swrve's messaging to be far superior to Localytics and really benefitted from the Eloqua integration so that we could control all our communications from the same platform