Where do I get the best return (based on energy consumption)? Hopefully this type of chart will answer the question.

(the unlabeled vertical axis is energy consumption (kcal))
At the moment, it's not much of a shocker. Gosh! Lengthy exercise results in more energy usage, but there are a couple of points here which I'll be looking to address.
The points are aggregated time/kcal figures on a daily basis. So each Bike point is actually two sessions (well, most are. Cycle to work, cycle home again). If I break them out into their constituent parts there may be more clustering.
The other option is rather than plotting cumulative energy output, I can output kcal/minute. I don't even have a sample display for that one yet as it requires more effort than I'm prepared to put in on a Friday night. It might not be any more interesting but I won't know until I try it out.