Smaller cattle are in theory more efficient than larger cattle at turning feed into beef. I say theory, because obviousely when it comes to an individual cow, there might be a larger one that's very efficient and a smaller one that wasn't and it might not be true for those two specific cows, but on average, the smaller cows are supposed to be more feed efficient.
The problem with the lowline angus cattle is that they are, as you said, "all the rage" right now. Which means they're expensive. So, if your just looking to raise a cow to feed your family, I think there are better options. If you want to start a business... well I think you'd need to do a ton of research into the cattle market etc to know what the right animal for your circumstances is.
How much land / pasture do you have? What is the condition of those pastures, and more importantly their fences? Talk to your extension agent and find out how many acres it takes to support a cow in your area - some areas it might be as low as an acre. Others it might be 5 acres or more per animal. Your extension agent will know.
If you decide to go with smaller cows, you should at least take a look at dexters. They're much less expensive, readily available and probably just as feed efficient. Other smaller cows are mini-herefords and zebu. Also, you might look at "square-meaters" which are small but don't consider themselves to be miniatures.
If you're just looking to raise a calf to eat later, you might consider bottle raising a dairy calf. You can usually get a dairy calf quite inexpensively. A lot of work, but I understand it can pay off quite well as a source of inexpensive beef.
Best of luck!
Oh. Another good site for cattle information is
www.cattletoday.com. They're a very knowledgeable group. Read there for a few days and you'll learn a lot! I sure did.