I had a solar water heater in AZ with an 80Gal tank and LOVED IT! I have a 50Gal tank with a booster electric tankless in ND and it's OK after about the first 5 minutes in the shower (software is very slow on tankless for safety reasons) I wouldn't recommend a downline tankless, put it upstream of the tanked water heater (though in my situation this was alot less cost efficient).
10/1/11: Bought the perfect house;
11/1/12: 10k & 200 hours
08/1/13: 30k & 400 hours into the perfect house
12/1/13: 35k & 500 hours
02/1/14: 37k & 550 hours
08/18/14: 38k & 650 hours it's starting to come together or maybe I'm coming apart