Hi Salim, the frequency is indeed a good indicator which of the sequences are hot candidates for biophysical characterization. Just because you mentioned M fold: I was involved in a project on solving the crystal structure of an aptamer bound to its target. Interestingly, not a single base pair was predicted correctly by M fold, so don't pay too much attention to that. It can be pretty misleading. If you are interested, compare Figure 2 (actual secondary structure) and Supplementary Figure 2 (M fold prediction) of the paper: https://www.nature.com/articles/ncomms7923#Sec22

Thank you