Classic car values are impossible to predict. One one hand, both cars' values might increase at pretty similar rates - on another, an Elf might get used in a big TV series and see prices rocket (think what Life on Mars did for Mk3 Cortina values). If you want to try and be practical about it, make an honest assessment of your cars (or have a local garage do it). What bodywork issues are likely to face over the next ten years? Or will one need an engine rebuild? I imagine parts and running costs for both cars are similar, but if one model looks like it will need a full restoration then that's going to be an expensive bill... unless you're handy with a MiG welder. An optimist could say that the 'Mini with a boot' Riley Elf is due to have its day soon, while on the other hand you could say that values have already peaked. I know they're both very different animals, but (assuming they both get a clean of health) I'd just stick with the car that means the most to you and that you enjoy driving.