Let’s start with chainrings as, although they’re not a set-in-stone choice, you’re not going to be swapping them back and forth regularly. You’ve essentially got a choice of three common set-ups: a standard 53/39, a ‘pro-compact’ 52/36 and a compact 50/34.
Having a larger big chainring gives you a bigger gear for flatter courses. The downside is that, if you hit some hills, the corresponding larger smaller chainring may leave you grinding rather than spinning.
Why can’t you have the best of both worlds with, for instance, a 53t large chainring paired with a 34t small chainring? Unfortunately, front mechanisms can’t cope with such a big differential.
For all-round riding I’d recommend the ‘pro-compact’ 52/36. But before heading out to buy new chainrings, check the Bolt Circle Diameter (BCD) of your crankset as this could affect the choices available to you.
For your cassette, 10- and 11-speed now give you the option for incredibly wide ranges, but this doesn’t mean you should rush out and buy an 11-32 cassette. Yes, this option gives you the best of both worlds of a big gear for flats and descents and a granny gear for spinning up steep climbs. But, even with 11 sprockets, there’ll still be some significant jumps in the cassette, which will disrupt your rhythm and make it difficult to maintain a constant cadence.
For your do-it-all set-up, my advice would be to choose an 11-28 cassette. You’ll still have your big gear, the 28 will get you up all but the steepest climbs and the jumps won’t be so pronounced.
Changing a cassette isn’t hugely difficult, so you can tweak your set-up to suit different courses. For example, if you know it’s pancake flat, a close 11-25 cassette would work well. Just remember to check that your chain length
can accommodate the resulting change if you’re putting on a wider spread cassette.