emerald and ascher with round brilliant accents for rings, round brilliants for everything else. i like aschers very best. it really depends on the piece, shape, finger size etc. in general, as big as you can afford while not sacrificing the other c's too much is always best. my ideal ring is 1.5-2.5 carat ascher with pave diamonds in the gallery and band (a la tacori) or more realistically a three stone emerald cut ring with a 1ct center stone and .25 ct side stones (one from my orginal engagement ring). i *really* want some 1ctw diamond stud earings right now, but those will have to wait five years or so. i heart diamonds.
For my dream engagement ring I would like a Huge (3-5 carats) center princess diamond and pave all the around the band! Sparkles everywhere! I also love the antique look with lots of attention to detail!
My favorite cut is the Asscher. I think 3 carats is the perfect size, it's a deep cut so a lot of the weight is in the belly. I have a 3 stone ring that is all round brilliants, the center is 1 carat, the sides .50, and I love the proportions, and it is so sparkly. The Asscher is more understated.
I like the emerald cut and oval shape. The princess is "in" right now and it is pretty but trendy. Even much more than a bag, a diamond should be classic IMO. I thought I wanted an emerald cut but really wasn't thinking about getting a diamond. My husband surprised me with an oval cut, plain tiffany setting, on our wedding day. He really wanted me to exchange it if I wanted something different and we looked at options. I stayed with what he had selected (except moved from the yellow gold he had picked to platinum). I really do think it is perfect as it is so simple, timeless, but the oval shape makes it just a bit unusual. Not saying bigger would not be better, but 1.2 carats is a good size for every day, and I am small. It is D color and VS-1.