I wonder how much of that has to do with its opaqueness.
Well, you’re just mean, aren’t you?
I like the blue and purple stones the best; I’d have to say February/Amethyst, September/Sapphire, December/Blue Topaz and March/Aquamarine are my favourites. Garnets or rubies sure do make a dramatic piece of jewellery, though. I don’t really consider turquoise a gemstone, either. I think you’re onto something, Santo - my least favourite gemstones are the opaque ones. A gem should be crystalline and sparkly to me.
Diamond, baby!
The bigger the better.
(Diamonds are a girl’s best friend, you know! 
)
My birthstone is sapphire, but I so love diamonds. Emerald’s good too.
Just like me! Though I’m not sure if I like diamonds better than sapphire. Blue is awesome, and sapphire’s a good, deep blue, not a wussy turquoise blue. Er, no offense to turquoises.
i don’t like purple and i am a feb. baby.
thankfully, i have the name day fall back which is sept 30th. i like blue so sapphires are a nice alternative.
my ab. fav. is the opal. love the opal.
the aquamarine would be my second choice after opal.
Given the ridiculous amount of gemstone jewelry I own, I was thinking that I must have pieces with every birthstone, but it turns out that’s not true:
January (garnet) - I only recently started purchasing garnets, but they are one of my current favorites.
February (amethyst) - I have quite a bit from the 80’s, but except for one of my favorite rings, which has an odd-shaped amethyst stone, I tend to think of it as jewelry for young, carefree people, rather than as serious career-wear. Maybe that’s just because of the particular time I purchased my amethyst.
March (acquamarine) - Too pale for me.
April (diamond) - I don’t wear diamonds because of a number of issues hashed out in other threads. I don’t want to hijack here.
May (emerald) - I don’t like bright greens – they don’t look good on me.
June (pearl) - My current favorite gem. I’ve become a little obsessed. Today I’m wearing a pearl ring, pearl drop earrings, and a sweater studded with faux pearls.
July (ruby) - I own a few that I like, but I prefer the really rich, pink color that is generally too expensive for me.
August (peridot) - My birthstone. I’m not a big fan of green, but I do have a bit of peridot because it’s my birthstone. Really good stones in certain shades can be very nice.
September (sapphire) - The only sapphires I own are fake. I like the rich blue color, but almost all sapphires available in my price range are too dark.
October - Opal. I have a bunch of fake opals. I was into them for a while, but now I prefer pearls for a similar glow.
November - Topaz. As I mentioned in the other thread, I have a few citrine pieces, but they only go with specific colors in fashion. I have a lot of white and blue topaz which I really like.
December - Zircon. I don’t own any, although I do have the alternative, blue topaz.
I’m a big fan of the opaque gemstones. My all-time favorite gemstone is lapis. But if I had to pick a birthstone favorite, I guess it would be pearl.
I’m July. I like smaller rubies(and thank god for that. Like I’m liable to get large ones!). But I prefer blue or green to red, so it’s sapphires and emeralds for me. I also like opals, my daughter’s birthstone.
I really, really don’t like the look of turquoise. I see it in some southwestern jewelry and in that medium it looks fine, but I still don’t like the milkiness of it. It’s such a garish shade of blue. I like the turquoise mixed with some reddish variegated stone (another type of turquoise? I dunno), but again, in very small amounts.
I don’t wear a lot of jewelry, period, and I don’t wear a lot of jewels. I do wear a sapphire and diamond ring constantly–it was my sister’s. It’s not her birthstone, either (we shared the same birthdate), but she liked blue stones, too.
February here, and I like amethyst alright but my favorite color is green. I like deep emeralds and peridots (but don’t own any). Pearls are another favorite, especially paired with garnets (my husband’s birthstone). I think it’s a very classy combination. I’m picky about the hue of gemstones though; I prefer very deep and rich colors.
Actually, I prefer my June birthstone as a pearl. I have always loved pearls!
Isn’t Feb amethyst, anyway??? 
(ETA: oops- I see the correction’s be made!)
October here and while I have a number of opals, I rarely wear them. I am hard on jewelry and I’ve chipped or scratched several opal rings in the past. Also, I prefer faceted stones.
I love diamonds and sapphires best.
My birthday is in June. Lucky me that pearls are my favorite. After that, I’d go with January (garnets).
I’m May and I love emeralds. Amethysts and opals are also very pretty. I have a very cherished ring my husband’s grandmother gave me when I married her grandson. The ring is an opal set with diamonds. Her mother gave it to her to celebrate her engagement to my husband’s grandfather on her 21st birthday in October of 1942.
Opals are by far my favorite. They are so mystical and enchanting. Their color is so deep and beautiful.
I’m another February, and I do love amethyst, but not so much in jewellery. I definitely like garnets most. Red is my favourite colour. I received a necklace on my 18th birthday with a red cubic zirconium & drop pearl pendant which I wear pretty much every day. It’s gorgeous and means the world to me, plus it gets me lots of compliments.
Heh. I am opal by birth, but using the name day method I’d be aquamarine! Neither one is a favorite but I don’t mind them either.
My true birthstone is the diamond, which is fine by me, but I love the look of peridot (August). Also, blue being my favorite color, a sapphire (September) wouldn’t be bad, either.
I’m a May baby, and that works well for me, because emeralds are my favorite gemstone. I even have them on my wedding band, and have never had an issue with damaging the stones. I also really love pearls.
Thirded. I hate diamonds and I will never own another one. I much prefer sapphires or opals.
I’m June/Alexandrite, and I LOVE it. But I can’t afford natural stones, so I’ve got a nice synthetic right now. Some day I plan to indulge in some lab-created ones. I also adore the alternate birthstones for June–pearl or moonstone.
I highly favor non-opaque, colored stones. Any color. I love them, pretty much all, and the deeper and richer the color, the more I love them.
My actual birthstone is the peridot, which I quite like in silver and white metals. Yellow gold washes it right out.
My favorites are turquoise and aquamarine, becuase they’re flattering on me (my eyes can go bluer or greener with certain shades). And of course, the classic pearls.