Based on sales it's 1: US (8.73 Million), 2: Japan (8.06), 3: Europe (4.91). (this is vgchartz data so not completely accurate but it gives a good indication.)
Wario Land games sell the most in the US, while Wario Ware games tend to sell the most in Japan. Of course there are some exceptions like Smooth Moves which sold the most in Europe.
There are also factors like the amount of Nintendo systems sold, which gives the US a huge advantage over Europe and especially Japan.
I say Wario is relatively most popular in Japan, followed by the US. He's least popular in Europe but Nintendo in general is less popular in Europe