As the next "Long Term Release" of Joomla is on the way, we now develop all new websites in Joomla 3.x.
The only exceptions to this are where the functionality or required extensions are not yet available for Joomla 3.x.
Theoretically the migration from Joomla 2.5.x to Joomla 3.x is easier than the migration from Joomla 1.5.x to Joomla 2.5.x, but it is in most cases far from a "one click upgrade".
However, after a good bit of trial and error, combined with countless hours researching various Joomla forums, we have now successfully migrated a handful of sites across to Joomla 3.x. We will therefore going forward migrate all of our customerbase across.
We also welcome anyone with either Joomla 1.5.x sites, or Joomla 2.5.x sites to come forward for a free assessment and quote for such migrations.