Yep.

It all depends on the intention of your statement. Because it's a conditional statement (so zero, 1st, 2nd, or 3rd) that conveys certainty, anytime you use a verb such as 'think', 'guess' or 'suppose' as a qualifying verb, you are lessening that certainty. To my ear, the following would be better: 'I suppose London would be my first choice if I were to live in England.' 2nd conditional - uncertain, hypothetical situation and its likely result. Of course if you remove the 'suppose' you could write: 'London is my first choice if I live in England' zero conditional - this is true if that thing happens Hope that helps

I suppose London would be my first choice if I lived in England.