After version 9, I recommend to those clients who need to use Acrobat (for 100% compatibility with business partners) to forget the Mac version and use the Windows version. Most them run a Windows virtual machine all day long anyways (for MS Office, Exchange, Quickbooks, etc) so they are used to mixed environment. From a practical standpoint, it's fine, but from a philosophical standpoint, it irks me to have to say to clients they are better off running a Windows app than a Mac app, and it's not like this is some oddball business requirement... this is PDF, which irony of ironies, Apple was a big part of making it a standard document exchange format in the first place, with its adoption of Postscript, Display postscript and making Adobe so successful in the early days of Desktop Publishing.
For those that can get by with lightweight PDF functionality (annotating, adding signatures), the basic free version of Nitro PDF on Windows works well; it's more than a reader, but doesn't have all the kitchen sink features of the high end.
I've tried PDFPen Pro and others for the Mac, to date, IMO, they just don't cut it (yet). Compatibility issues increase as the complexity of the documents increase, and my clients can not afford the embarrassment of exchanging files with partners that do use Acrobat, which don't look right or sometimes don't even load. And for the price of PDFPenPRo, it's almost the same as getting a license for Acrobat for Windows, so may as well go for the Acrobat for Windows and eliminate the file compatibility issues.