My experience of One World miles is that unless you have a lot (like >100,000 miles), then they aren't much use. Reason being that you will only afford domestic/Europe flights - thereby meaning that a One World reward flight works out as the same sort of cost as an advanced purchase Easyjet flight (for example). This is bearing in mind that your reward flight still incurs taxes/charges. The only time I found a short reward flight to be worthwhile with BA was when they covered the Loganair Scottish Island flights up until a few years ago. As an aside, BA is very tight with awarding miles, so collecting miles is no mean feat.
Therefore switching to collecting Star Alliance miles has proved far easier and less costly and resulted in a number of intercontinental F class reward flights on my part. Something that I wouldn't have got close to with BA.