Avoid jelly, and always read the reviews. This will save you from most mistakes. Remember that bodies vary, so when something requires a specific fit, like a dual stimulator or rabbit vibe, it won't always work for everyone. Keep your dual stimulator purchases either cheap or adjustable until you have that figured out, then take the toy that fits to the computer screen for exact comparisons when considering future purchases.
I think the best things in my collection are the Pure Wand, the Little Chroma, the Form 3, and the Lelo Iris, but your mileage may vary. I also really love glass pieces. I'm the biggest fan of the Little Chroma in these parts, and some people find it flat out boring, but I find the pitch of the vibrations to be too perfect for words and compare everything else to it.