Hi Tan, I didn't have expanders but immediate reconstruction with silicone implants. My plastic surgeon went through all the options with me prior to the surgery - has your surgeon done this with you? Anyway, what I gathered from the discussions is that the round ones give a fuller look and are good if one wants to go "big" on top, downside is that they may give bit of a fake look (think of fried eggs, heh..), especially on a slim body. My surgeon & I agreed on teardrops for a more natural look (I have a slim frame) and the modern silicone implants are not too bad as they are quite soft and won't leak into the body if they should rupture for some reason (which is unlikely). The silicone ones also come in smooth and textured varieties, with textured one giving a more natural feel. There are saline implants available too and whatever you end up with should be the best match for your own body size and shape, e.g. to me the saline implants looked a bit saggy but probably would look fine in the right type of body. PS. despite the name "teardrop" they don't droop so can easily go braless :)
Wishing you all the best to your implant surgery Tan. If you have any more questions I'm happy to help! Annie