I think one of the best cultivars of Cornus kousa is 'Miss Satomi' (also known as just 'Satomi'); this cultivar has reliable pink bracts regardless of stress. It is fairly free flowering, and makes quite an impact.
|Cornus kousa 'Miss Satomi'|
|Cornus kousa 'National'|
There is one Cornus that I don't rate very highly, despite it being quite popular. Cornus 'Norman Haddon' is a hybrid of Cornus kousa and C. capitata, and it is the latter species that can prove temperamental in all but the most favourable parts of the UK. In some places it thrives, but in many more it struggles; I would always recommend C. kousa 'Miss Satomi' instead.
Flowering dogwoods are fairly straightforward to grow in principle; lots of sunshine and a soil that doesn't get too wet or too dry and you should be OK. That said I heard some wisdom from that legend of gardening and general nice guy Roy Lancaster- different cultivars of Cornus thrive in different areas. With this in mind you might need to do some research to find which varieties suit your area... failing that just throw caution to the wind and buy either 'National' or 'Miss Satomi'!