You have to register your order of preference for all participating organizations meaning, for all 20 banks & ECGC.
As candidates, we dont have any parameter based on which we can choose the banks.But many candidates are looking at the best public sector banks in india to make their choice.Even then, the list varies when taking profits, market capitalization & NPA ratio is concerned.
Recently bankexamsindia.com came out with a survey of the popular public sector banks in india at http://www.bankexamsindia.com/2012/11/the-best-public-sector-banks-in-india.html
It is mainly based on the popularity of the bank as bank job aspirants don't look at intricate details of that specific organizations performance while opting for that bank.
Also they have prepared a table containing probation, salary & bond conditions for each public sector bank.Based on that also, you can select your preference because if you dont want to join a bank with bond, then dont choose such PSBs as 1st choice.See the complete list at http://www.bankexamsindia.com/2013/02/bank-salary-probation-bond-details.html