Which scaling size is better? [0,1] or [-1,1] for LSTM?
I think both scalings can potentially behave well. The important matter is to put all the features in the same range, otherwise some features will add up more in the first linear transformation of your layer (remember that any neural network is a linear transformation and a non-linear one), which is undesirable, and will hinder the learning.

Best option is then to try both, and take the one that gives best performance.