I am currently reviewing IPS with their demo (again) as v4.3 has been released so this is my thoughts
Basically my site needs:
Forums (XF v1 has a great html based template system, v2 is more XF syntax based and requires a big learning curve, IPB requires learning curve)
Gallery (both XF v1, v2 and IPB have this but XF v2 I think is the better one)
Downloads (both XF v1, v2 and IPB have this - I am told IPB downloads is the better one)
Clubs (XF v1 and 2 has an addon but IPB one is far superior)
Classifieds (XF v1 has an addon but not v2 - IPB have an incredible addon available for this
HERE)
CMS (For articles etc - XF v1 has an addon but not v2 - IPB has one built in)
Shop (I currently use CS-Cart which is more powerful than the IPB Commerce - I have an XF-CSCart Bridge with SSO developed for XF v1 so it needs to be upgraded anyway whether XF v2 or IPB)
Expo (A section to list suppliers - see attached screenshot - XF v1 has an addon but not v2 or IPB)
Showcase (XF v1 has a Showcase addon only, XF v2 and IPB doesn't)
As per a comparison on smaller features it is very much swings and roundabouts like IPB can allow Admins to use HTML, XF doesn't (but does have a a currently non workable addon)...
The likelihood of XF addons to be developed to suit my needs is either not going to happen or will take a long time before anything is available
I have made the huge mistake and upgraded my current site a few months ago to XF v2 so a roll back to v1 is not really possible easily
@Bob has some great addons to suit but not currently for v2 so they could be a year away. A great Classifieds addon is a MUST but that may never happen or take a year to be useable if one is being developed.