We are in the process of potty training my 18-month-old twin girls.  Below is my review of this item as well as the other items we tried.

Handcraft Girls 2-6x Toddler Hello Kitty 7 Pack Panty, Multi, 2T/3T - Five Stars
Highly Recommended, Very Cute
These are really cute bold-colored panties.  They fit well and include a mix of light and dark colors.

Others:

Fruit of the Loom Girls 2-6x Toddler 6 Pack Wardrobe Brief, Assorted, 2T/3T - Five Stars
Highly Recommended, Best Deal
These cute little panties are hands-down the best deal out of the five types I bought.  Each pair has trim with multicolored stitching around the edges and the rainbow stripe panties look retro.

Fruit Of The Loom Girls 2-6x Toddler Boyshort, Assorted 3 PK, 4T - Four Stars
Cute Panties, Run Small
With potty training, there's a lot of time spent in just panties.  These work well for that because they look more like little shorts.  The other reviews are accurate regarding how these run small and don't stretch.  My girls wear 2T and 4T fits perfectly.  They are adorable on!  The pack I received included two prints and one solid color.  I think they'll also work well under dresses that don't have bloomers.  However, the bright prints will show through some light colored pants.

Carter's Girls 2-6x Rainbow 2 Pair Pack Training Pant, Multi, 2T - Four Stars
Super cute, but pricey and not absorbent
These panties are so cute, with cheery prints and lace trim.  That said, the extra padding won't really help if your little one pees in his/her pants.  It is also really difficult to tell the front from the back.  So, I'm not sure they're worth the extra money.

Gerber Brand 2 Pack White Waterproof PEVA Pant , 2T - Three Stars
Typical Plastic Pants
These are typical plastic pants that crunch and make noise.  I found that the Dappi brand vinyl pants are much softer.  Ultimately, I decided that these pants don't work for my purpose.  They make a line on my little ones' thighs and don't hold accidents in during naps.

Dappi Waterproof 100% Vinyl Diaper Pants, 3Pack, White, Large - Four Stars
Soft Vinyl Pants
This brand is much softer than the Gerber plastic pants.  Ultimately, I decided that these pants don't work for my purpose.  They don't hold accidents in during naps.  Perhaps they would work if I put them over something more absorbent than panties.