As already put by others:what is your sac rate; were you already short on air (if so with how many liters of air), are you still buyond when dropping your weight, etc.
These are a few questions that you should ask yourself. They might eliminate some configs.
My singles are steel 15l@232bar (3480l / 123cf), but mostly the tankfill is between 190-200bar (cold) (so pay attention when opting for a 200bar bottle, because you might end up with 170bar). For me this is more than enough for a normal dive in local conditions (cold, bad viz, etc).
I have also been diving a colleagues 12l@300bar Carbondive (ok, this adds to the price) and that was a very comfortable config.
Personally I wouldn't go for steel @300bars, as they usually add to much weight.
My advice would be to check for the carbondive bottles @300bar, if the price is not a key criteria.