I once had savings in an offshore bank that closed. Taken a long time to get the money back. For this reason, the majority of my savings are in GSB. I asked them to check for me several years ago how much of a guarantee they give and after checking with head office I was assured 100% of savings were guaranteed. I asked what if the bank went bankrupt (there was a brief run on the bank several years ago). They explained that for the bank to go bankrupt, the Thai government would have to be bankrupt. The government guarantees the bank.
If commercial banks went bankrupt there is a scheme to pay you one million baht. If you have 5 million or more you will not be happy.
I use SCB for salary deposits and ATM and have less than a million in several other commercial banks but I shift money to GSB whenever i need.
I also put money into their lottery account because I win an average of 1,000 baht a month plus annual interest.