Unless Avant Browser modifies IE's security settings (most notably ActiveX permissions) it is no more secure than using IE itself in many aspects, since it well uses IE!

Here's an interesting comparison between the heuristics test for multiple AV software.
http://www.pcmag.com/article2/0,1895,1850851,00.asp

There's no Norton in the list either, are you confusing it with Norman? AVG was not listed because it didn't detected the virus without a signature update.

This tests the AV software against recent threats, and is not definitive about the overall heuristics detection ability.