I'm impressed by how many women do not have to wear maternity clothes! If I now put on any of my shirts from before pregnancy, they won't even cover my belly button! That being said, I can still fit into some of my non-maternity maxi dresses that previously required heels.
I started wearing maternity clothes early, but that was mainly due to comfort rather than necessity. I also like to wear tight clothes, so it did not feel good to have something digging into my bloated belly. I bought a pair of demi panel skinny jeans from the GAP, and those lasted me well into my second trimester. They were my daily go-to pants. Now, I can only comfortably fit into full panel bottoms, yoga pants, gym shorts, and maxi dresses. TMI, but I even had to size up on my undergarments because my pregnancy ones were barely offering coverage of anything!
I started wearing my first maternity tops a bit after 20 weeks. I didn't really look pregnant before then (just bloated!), but the maternity pants were a necessity for comfort. You cannot tell they are maternity pants at all. I definitely say you should go for comfort. I felt so silly and embarrassed for ordering maternity pants when I was just barely pregnant, but as soon as I put them on, I was SO glad I did. I've had really good luck ordering from Motherhood Maternity. They have a few pant styles that come in longs, which I need, so I was super happy to find them. They fit like normal jeans whereas other brands I tried fit really baggy and droopy! I just remind myself (and my husband) that we plan on having more kids, so whatever maternity clothes I buy now I'll be able to re-use later on. I've only bought really basic staples (jeans, short, solid t-shirts, etc.), but my work attire is very casual. 
