Even though I Love my 4, for straight brush and up to medium vegetation clearing, I would take a BK5.
If including wood processing, chopping and batoning, I would then take the BK4.
Regarding the BK2, it is a Tank. Hell, someone has batoned it through a steel lawn mower shroud and an AC unit just to show what it can do...
Most people don't need to have that kind of durability, strength and weight. Go with a BK10 or better yet a BK12. Take a look at the following thread for a BK10 vs BK12 comparison.
http://www.bladeforums.com/forums/showthread.php/1080709-bk-10-vs-bk-12-picture-request
Knifeworks has the 12.
But, if I personally had to spend $175 on a fixed blades, it would probably be 3 Beckers; BK4, BK5 and BK16.
With those you would have your firewood procurement and processing, food prep (including the capability to break down animals as large as an elk or zip open a trout), camp work, a belt knife, and edc blade and clearing a camp site. All in one fell swoop.
Those
three should land you under $170, if you shop smart.
Fwiw:
I would venture to say that Most of the people who have purchased a BK7 first, end up going for the 9 and the 7 collects dust.