I spent a few years removing Celigo from NetSuite and Salesforce. The best way I can describe Celigo is that it is like the old school anti-virus programs which were often worse than the viruses... lol... It digs itself into the end system, making removing it a nightmare.
Boomi does the job, but is very counter-intuitive, and overly complex. You can't do everything from one screen, you can't easily bounce back and forth between tasks/operations/etc. And, sometimes it is very difficult to find where endpoints are used, as they are not always shown in their "where is this used" feature. Boomi has a ton of endpoint connectors pre-built (the most, I believe), but I have not seen an easy way to just create your own. Boomi also has much more functionality than just the integrations, if that is something that may be needed.
Jitterbit, my favorite, is ridiculously simple to use. You can access everything from one main screen, you can connect to anything (as long as it can reach out to the network, or you can reach it via the network - internal or external). Jitterbit has a lot of pre-built endpoint connectors. It is also extremely easy to just create a connection to anything you want. The win with Jitterbit is that it is super easy to use, super easy to learn, it always works, they have amazing support (if you need it). I have worked with Jitterbit the most (about 6 years), and I have never been unable to complete an integration task in less that a couple of day, max.