There are a few issues. By best browsing, im assuming you are talking about support for the browser.
There are very few nokia n series phones with great browsers. The n95, n82, n96 support flash light embedded in the browser.
However, nearly every e series and n series nokia have the ability to install a third party internet browser that has embedded flash.
You cannot install any actual computer browser on a phone. The only phones that have internet explorer are windows mobile phones.
The e71 has the standard html only nokia browser.. but you can install quite a few other browsers: opera mobile and skyfire for example. same is true with the e90.
Although im a nokia fan, im going to say pass on the e71. The keys are small, short battery life, terrible call quality, and dropped calls plague it.
The e90 is a nice phone, but its very thick and heavy. Nokia announced the e90 successor this morning at 03:15, the e97. The e97 has embedded flash in the internet browser. The rumor is that its due for production and sale in mid-late 09, and will actually be cheaper then the e90 is now.
now on personal preferance. It would be fantastic for nokia to adobt the trackball on blackberrys. I do not care for the dpad when navigating on my e51 or n95-3, because it skips a few links that are hard to get too.