When I first started I liked the idea if kits but since I really got into cross stitch I prefer buying patterns because I feel I get more variety to choose from. Besides, I dont have any major needle work shops near me and the standard craft shop has limited selection on the kits they offer.
I usually buy the kit to get the chart and always replace the fabric and floss anyway as most kits use lesser quality floss. I donate those to teens or whoever wants them to teach or learn with.
I think patterns personally. With the wide range of fabrics and even the over-dyed threads available Ive been having a lot of fun picking out the threads for my new projects. I see DMC has also increased their hue range of colors and weights of thread too.
I prefer the patterns so far, because sometimes I like to change the fabric colour, or any thread...and there is another reason, most of the kits come with aida fabric, and I love linen and evenweave fabrics.
Patterns, but usually bought, not downloaded. I had some experience with patterns half-done and discovered missing or unreadable parts. :L
Kits I dont like too much, because I constantly modify them. :)
When you are a beginner, it may be better to choose kits - so you do not have to worry about anything. Later on you will discover how you can convert designs to your own taste. I personally prefer choosing my own thread and fabric, but also do some kits when I find that the company made the choices that I would have made :)