I just downloaded the Opera Browser for my Windows Mobile 5 PPC - 6700. I am amazed by how fast and intuitive the software is.
I normally use the WM5 version of Internet Explorer (IE) and have been let down by Mozilla's Mini browser, Minimo. Minimo had the right idea of tabbed browsing and cool buttons. But when I went to a site that Minimo did not like it would randomly close and I would have to start all over again. Also the program ran very slow for a PPC with a 416Mhz processor and 64 MB of RAM.
IE also sucks (not as much as Minimo) since it too does not like certain sites and sometimes freezes.
My device is old but was ahead of its time when it was released (early 2006).
Conclusion: Opera Browser>IE>Minimo.
(Sorry Mozilla, I still love you for your Firefox and Thunderbird)