I am looking for something along the lines of a DPMS AP4 PANTHER for ranch use.

I'm new to the AR world and the number of possibilities is almost endless.

I want to buy a gun that has future flexibility. I have read / heard that certain brands have major parts, like the upper, that will not interchange with other brands due to pin size, etc.

Here is a list of manufactures, which appear to offer quality products:

DPMS
Bushmaster
Stag
RRA

What about Olympic? The price is pretty low compared to the others. I'm assuming you get what you pay for.

Is there anything peculiar about one of these brands that I should be aware of?

Please don't turn this thread into a vs. or bash fest. I'm just looking for some advice from guys that have been there / done that and don't want a $1000 ... 'oh crap what did I just buy' on my hands. I want something simple and reliable at a decent price.

Many local owners / gun shops have suggested getting an A2 upper. It seems to me a flat top would be a better long-term choice. Comments please?

you shouldn't go wrong with any of those, my personal preference for them would be in this order:

bushmaster
RRA
stag
dpms

and yes, pony up the extra $100 for the A3

Does that mean that any of the manufactures on your list would allow me to purchase a different brand varmint upper and it would be compatible?

Thanks in advance for your patience!

Quoted: you shouldn't go wrong with any of those, my personal preference for them would be in this order: bushmaster RRA stag dpms

+1

Quoted: Does that mean that any of the manufactures on your list would allow me to purchase a different brand varmint upper and it would be compatible? Thanks in advance for your patience!

You can swap uppers like its going out of style (but it isn't, of course).

Nathan