Help us plan - SE Asia edition (looking for advice)

My wife and I (mid 60s and pretty active) are considering traveling to SE Asia early next year. We have never been to Asia, and, frankly, it's a little daunting.

We're pretty independent, and generally shy away from organized touristy stuff. We've tried cruising and large group travel, and we just don't enjoy it as much as exploring on our own. Over the years, we've been successful in renting a car or taking public transportation.

That doesn't mean we don't appreciate learning more about the country's culture and hitting the things that shouldn't be missed.

I've been looking at Vietnam and Cambodia for several reasons. First, we're old enough to remember the conflict, and really would like to learn more about it from a different viewpoint. Secondly, from what I've seen, the people are generally welcoming of westerners. We also love food!

It sounds like visiting Vietnam and renting a car isn't a good idea. Plus, the area is so large, it'll be difficult to go there without at least some planning. That, and this is an unfamiliar culture tells me we need help.

An acquaintance told my wife she waas there a few years ago and did a tour through OAT, and had a great time. As I said, we stay away from tour groups, but a company like this might be a good idea, but the last thing we want is to travel in a pack with a bunch of other old geezers!

I know this is probably far too general a question, but I'm hoping for some advice from people who have been there.

EDIT: thanks to everyone who responded - you definitely helped!