Should i buy 24 months or 2t clothing?

i like to buy my daughter clothes in the next size up from what she is wearing at the moment to stock up in the size. she turned 1 on january 10 and right now is wearing 12 months, so i am currently buying her 18 months as i see sales or items on clearance. my big debate is once she starts wearing 18 months i dont know weather to start buying 24 months or 2t. ive heard they are pretty much the same. one thing my fiances aunt told me (she has 2 granddaughters who she obsessively shops for) was that the difference is that 2t is slimmer than 24 months. since her 2 year old grandaughter has always been very thin and a tiny bit tall for her age she would buy her 2t instead of 24 months. my daughter is thin but not tall for her age. so my debate is that i dont want to get her clothes that are too wide or clothes that are too long for her, i like her clothes fitting correctly. obviously i will compare the two sizes if i am interested in an outfit...but what would you do, or what size did you get when your child was around that size? did anyone skip 24 month clothing and just use 2t or did you use both?