The f1.8 and the f2 35mm Canon LTMs are quite distinct from each other. My observations are based on color photos taken on Sony A7 digital camera. If there is anything in particular anyone wants to have compared, even if only on Sony A7, please ask for it I may try to do sample photos
I'd say the f1.8 already is sharp wide open, but this sharpness is e.g. when focused in the middle limited to a quite small oval. strong light fall off. Corners on the same focal plane weak, only become ok @f8. However if focused at the corner sharpness is there starting from wide apertures! sharpness in the centre is gone then, my f1.8 shows very strong field curvature!
the f2 wide open is a tad sharper again and above all in a bigger area, even corners already quite sharp from wide open minus the very last corner which most likely is corner smearing of the sensor. light falloff is less pronounced. Corners again sharper when focused there, it also has some field curvature. ( I suspect that the field curvature could be due to sensor used, might be less pronounced on film )
bokeh of f1.8 swirly at wide apertures, f2 not so, oof highlights towards corners will be quite oval with both lenses
average barrel distortion, similar of both
the f1.8 gives pastel looking colours, the images have a distinct 'vintage' look. the f2 looks cooler, more modern.
the f1.8 easily looses contrast and flares, the f2 fares better
imo the f1.8 lends to being used at wide apertures for 'artistic' photos e.g. when contrast loss and flare even is desired:
https://www.flickr.com/photos/63016562@N04/23275595796/ but it's not a landscape lens
and the f2 is better for general use. see e.g. Ron Schefflers take @f8:
https://www.flickr.com/photos/ronscheffler/10385183326/in/photostream/ ( click arrows to see pics taken at wider and smaller apertures )
the search results for 'Canon LTM f2 35mm' resp. 'Canon LTM f1.8 35mm' at flickr
https://www.flickr.com/search/?text=canon LTM f1.8 35mm&view_all=1
https://www.flickr.com/search/?text=canon LTM f2 35mm&view_all=1
( most photos are taken with the lens, some photos of the lens, cameras used will be all kind, digital with smaller and FF sensors and film. )