I've never used either, but I'll throw out a few thoughts to ponder:

1. All software will have pros and cons, so *IF* you change, it is likely you'll really like some things, but be disappointed with other things.
2. From the posts that I've read through several forums and groups, UltraTax users seem to be slightly happier with the product than Lacerte users.
3. Yes, changing software really sucks, so it shouldn't be taken lightly or done without good reason.
4. Intuit's primary focus is for accounting software (Quickbooks) and tax Do-It-Yourselfers (TurboTax).  Thomson Reuter's primary focus is tax professionals.