Each script has their merits.
This is something neither group can get through their heads.

First let's go over something called "Perl quality".
This is the mentality of the Wakaba users. They believe that their script is best because "it's simple, Perl, and not crap" (Quotes from previous posts in this thread.)
They seem to hate anything that isn't Wakaba. Let's compare them to oh... Arch Linux users.

And then there's "PHP mentality".
This is the mentality of the Kusaba/Futallaby/Pixmicat/Tinyboard users. Most imageboards are written in PHP, using MySQL and GD, so there are more out there, and they all have their pros and cons too. The users want something that just works™. They don't want to have a page with no details on errors, they want to know how to fix things. Let's compare them to the Ubuntu Linux user.

A common argument for Wakaba/Arch users is that the rival (Kusaba/Ubuntu) is bloated. As someone who has worked on and developed my own board script (not releasing it here.) in Perl as well as a board in PHP, I can say that yes, Kusaba is bloated. 3 MB is a bit much for an imageboard script. However, Wakaba users are a little lacking in features as well... can anyone say they banned anyone from their board? So it's a trade-off between light-weight or fully-featured.

A common argument for Kusaba/Ubuntu users is that the rival (Wakaba/Arch) is difficult to learn and use efficiently. As I stated above, I worked with both. And yes, a nice error message from Wakaba would be nice, other than the "500 SERVER ERROR" shit I get with Perl because Apache haet Perl. PHP is like the duct tape of the Internet - there's lots of uses for it, you can easily learn to use it, but it doesn't really hold up well under intense load.

Perl is more like electric tape - strong, and will hold up under pressure, but one screwup and you're fucked.

tl;dr Go with whatever one feels right, OP.