I've owned 2 dobies back to back, lost my last one in October last year. They were both fabulous dogs.
Only owned bitches so not sure about the males however both my girls were super affectionate (especially my last one who thought she was a lap dog!!). When they're with you they like to be near you, usually being patted. However I was able to leave mine for periods of up to 5 to 6 hours without a problem.
Exercise wise, they like at least 2x45 min walks per day but if possible one longer walk of around an hour and a half and a shorter 2nd walk. If they are exercised properly they are couch potatoes and love lying sleeping.
Both mine were really greedy and got through tons of food.
My first dobie; we had from a pup so she was well socialised and got on fine with other dogs, my second was a rescue at 2 who had missed her socialisation so could be hit and miss with other dogs although she got better as she got older and when we adopted another pup (not a dobie) she absolutely adored her!!
Very strong and quite stubborn although intelligent and relatively easy to train. Not too destructive either.
Health wise; both my girls lived until they were 9.5 years, first died of heart failure and the second had cancer.
They aren't easy dogs by any stretch but I love them and I miss mine terribly!!!