Event Registration Tools

Looking for recommendations for a reliable, flexible, customisable event management system for registration, abstract management, marketing with the ability to create multi-day, multi-stream, multi-faceted events from 100 up to 1000 delegates per event. Options for delegates to log-in to manage their preferences but also the option to switch this function off. Onsite check-in, multiday check-in etc
Lots more but keen to hear who you use?

Eventbrite has integrations with many different solutions that might help meet your needs, like Boomset for multi-session management or Sched, to allow delegates to log in and create a schedule. There are lots of integrations for marketing too.