Depends on what you want. In general Olds the Olds is a reliable motor, but they have oil return problems when run unmodified at WOT for very long (more than 30 seconds or so). Essentially they are famous for pumping all the oil to the top end. loosing oil pressure and cratering the lower end.
If you are looking for a family boat to ski and tube with I wouldn't hesitate at all to buy an Olds. If you want to go 70+ or do a lot of performance improvements it is more practical to go with a BBC.
Do a search for "oiling problems" on this forum, or go to www.realoldspower.com and search the "Olds powered boats" forum. You will find out all about the oiling issue and how to fix it.
That said, there are some awesome and fast Olds powered jets out there, it just takes more work and $$.