Many investors focus myopically on dealing commissions. But stock brokers levy a wide range of costs and some will promise low headline dealing rates, only to claw it all back through high currency conversion costs or excessive account management fees.
Read the guide to how stock brokers charge and compare costs in the detailed stock broker comparison tables for the UK, the US, Hong Kong or Singapore. Try to get a feel what it will cost you to run your portfolio over a year, rather than just the price per trade.