Actually, I would strongly suggest to upgrade add-ons first, then EE. This isn't only for Solspace add-ons, but any add-on for EE. Make sure you update your add-ons to the latest version available for EE1 first, then upgrade to EE2. Sometimes, you need to then upgrade the add-ons to the latest version available for EE2.
This usually gives you the smoothest upgrade path to having your add-ons working correctly on EE2. Moving to EE2 while still using an add-on version that was EE1-only (at the time of the add-on's version) can be a painful experience.
Of course, also make sure you make backups at every step, in case you need to backtrack to a previous state. Reading the upgrade instructions for each add-on, just in case there's a special requirement, is also highly recommended.