I sewed clothes for a long time before I ever got into quilting. IMO quilting is easier.
You've gotten lots of great advice, so I won't beat a dead horse. One thing I had to really get used to is the different seam allowances- 1/4" seems really tiny compared to 5/8".
I would advise using some type of cotton fabric for your first garments, you're used to that. Also if you have a serger or overcast stitch on your machine, it's useful to go around the edges of your pieces to prevent fraying later on. They do make fray check but it's rather pricey and won't last too long. It can also help in not having your pieces stretch out of shape too much.
And garment sewing is a definite "pre-wash your fabric"! You might like the look that shrinkage gives in a quilt, but I guarantee after you've spent time sewing clothing it's not so great when it doesn't fit! Ask me how I know this.