You can almost always tell a top-down sweater because it has raglan sleeve shaping. Almost always.
Thing is, you get a raglan line because the increases (from the neck down) are centered over each other. If you don't center the increases -- make the increase in one row at the beginning or at the end of the increase in a previous row -- you create a visual seamline in any shape you want by increasing 'to the sleeve' or 'to the fronts' or 'to the back'.
I am starting a cardigan at the back of the neck, and it will have a saddle shoulder visual seamline, which looks more dressy than a casual raglan line. The advantages to top down include:
1. I have a limited amount of yarn and want a sweater from it. Dealing with the important stuff first, I can handle shorter sleeves or a shorter length and still have a sweater I like at the end. This way, I use as much of the yarn as possible and have virtually none left over. And even if I have plenty of yarn, working in one piece from the top down means I can make the sweater as long as I want, without any angst about running out.
2. Using a tape measure, gauge isn't the most important information to start with. In crochet, what you measure is pretty much what you get, since your stitches aren't restricted on needles. So my approach deals a lot with numbers and measuring. Some people don't like this; I am one of those who find this comforting.
The yarn I am using here is called Crespo, a cotton/silk/nylon blend in a light worsted weight (recommends #6 needle and 5.25 sts per inch for knitting). I have 8 balls of it, at 125 m per 50 gram ball -- about 1000 meters in all -- and I want to make a size 12-ish cardigan. I am using a size H hook. My pattern stitch of choice: I call it sweater stitch or single crochet lite --
Over an odd number of stitches, sc1, (ch1, sk1, sc1) across. Row 2 for pattern: Ch1 to turn. Sc1 in last sc, (ch over ch, sc1 in next sc) across.
I will have pictures in a few days.