Nowadays Perl/Tk looks different on Win32 and Unix. You'd be hard-pressed to tell it appart from native widgets.
For my part, I had to choose between Wx, Tk and Win32-GUI lately for a windows app (my first GUI app ever!), and I chose Tk because the relevant *Perl* documentation is more extensive (there's even several books on the subject) and it's the most used so lots of support is available. Win32-GUI is the worst with regards to documentation (almost non-existent) and I quickly discarded it. Wx is somewhere in between (mostly it tells you to read the C bindings!)
Wx seems to have more widgets but it also seems a bit more complex and to require more actual code to accomplish something. Then again, there's tons of Tk widget modules on CPAN, so perhaps Wx doesn't really have an advantage in this area. In any case, I was able to find a suitable Tk widget for all my needs.
I did run into a few problems with bugs in some Tk widgets, but they were easy to deal with (a quick google search turned up code to fix the problem). I don't know how Wx fares in this regard.