Our entire team relies on Mixpanel. We made the switch from Google Analytics only because it allowed us to see more personal and identifiable data. We really needed to start tying each user to their own data, and Google Analytics couldn't do that.
We moved away from Google Analytics to Mixpanel recently, but it's still a part of our system as a relic.
When our Salesforce license runs out we'll use Insightly. It's just lighter-weight. All of the tools that we subscribe to and are switching to are much lighter-weight. Anything that is heavy takes longer for new people to use. I'd rather sacrifice features and be able to bring people in and out as I need them.
We chose Sendy for its pricing. It's good enough. It takes a bit more engineering work than a MailChimp, but we wanted something a little more like Marketo where you can get in there and make something complicated. MailChimp and Constant Contact are very basic. With Sendy, you can do those complicated things and it has a much lower price than Marketo.
We love the lightweight tools. We tried JIRA and Asana, but it was too much, even though we do software development. For the size of our team, Trello is perfect. I intend to stay with Trello until we hit 20 people.