The thrifty-fifty. For £90 this about the cheapest, smallest, lightest Canon lens you can buy and in some ways it's an absolute bargain.
Based on quite old but good optics, there is very little to say about this lens. It's all plastic apart from the opics. Has no IS, no ring USM (no USM at all), no full time manual. It's even a job getting a hood attached without a special adapter.
While it has a pretty fast aperture it is quite soft wide open. Stop it down to f/2.8 or beyond, though, and it produces very sharp results, better than lenses many times more expensive. Unfortunately that aperture only has 5 straight blades, so the pentagonal highlights aren't very appealing.
The main downside with at least our copy (and seemingly many others) is the woeful autofocus accuracy. The micro-motor focusing isn't very fast or quiet but I could live with that. The almost completely unreliable focus accuracy at wide apertures isn't. It fares better using contrast-detection focusing in Live View but that's not always appropriate.
Bought as essentially a toy lens to mess around with it will remain as a toy for experimenting with. If you get a good focusing copy or can live with using it at f/4 or higher you will get a fantastic little lens.