Water Heater Woes

Well, apparently the water heater is jealous of all the attention the air conditioner has been getting lately, because it continues to cause me problems.
I called the plumber to check out the thermostat a couple of weeks ago, and he replaced it (no sweat, 20 minutes and 40 dollars).
But then a couple of days ago it began leaking from the top, right under under the valve that turns the water on and off to the heater. The water was running down the back and into the drain pain and then dripping on the floor. Tommy got up on a chair and tightened the valve and it stopped running and we thought that was the end of it. I put a bucket underneath to catch the residual water runoff that was still dripping on the floor and then walked away and forgot about it.
Again we come to the beginning of the weekend and again, we are strapped for cash, when standing at the stove in the kitchen I hear a suspicious little "drip". I look around the corner and see that the little trash can is full to the top with water. This alarms me because it has been three full days since Tee fixed the valve. This should have dried up by now. Apparently that residual drip was not from the top of the water heater, but it must have been coming from inside the water heater. Again I called the plumber and he came out and confirmed that the water heater has ruptured. We are going to have to buy a new one.
That said, I decided to do some more research on the Internet. I have been thinking for a long time that when the water heater finally kicked the bucket I would go ahead and get a tankless. They are supposedly more energy efficient (thirty percent savings over the tank style for gas, and seventy percent savings for electric), supposedly you never run out of hot water, they take up less space, and if you get them installed by someone who knows what they are doing and you get a quality brand they can last up to twenty years.
So I got on my computer and immediately became inundated with all kinds of information that clogged up my brain in a hurry. I've heard of MPG, but how about GPM (that's gallons per minute). In order to make a good decision about which kind would be the best for your home, this is something you need to know. Do you need a whole house heater that can run more than one major application at a time, such as a shower a dishwasher and a sink? ( A shower runs about one and a half gallons per minute, ditto, for the dishwasher, so for two applications you would need something that runs at least three gallons a minute. As much hot water as we use, based on the six hundred fifty dollar electric bill we got last month, I think we need one that heats about seventy five GPM) Or if you have a smaller household, can you just get by with something that will only heat enough water for one application at a time, such as a dishwasher. After you read that line two or three times, then you move on to the electrical. How many amps do you need? Do you have enough "amperage" (for lack of a better word) in your fuse box, or do you need to have a special fuse box made just for the water heater? How cold is the weather in the winter where you live? Because the difference between the low temperature outside and how warm you want the water determines how hard your water heater is going to be working to keep your shower hot. And whatever you do, DON'T let the plumber attach copper lines to your steel applicance, or you will have corrosion and failure in five or six years, And by the way, you will have to have both a plumber AND an electrician out to install the thing after you finally decide which one is best for you.
Anyway, I'm taking a roundabout way to say that I was somewhat intimidated by all the information.
I haven't made a decision, yet. I would really like to get a tankless, despite the fact that I feel like I am in over my head. The problem of course is the cost. I found one I really like but it's a thousand dollars, BEFORE the installation. Now THAT'S intimidating

Post script.
I intended to buy a new one right away but the dripping slowed down and finally stopped, enabling me to save a little bit of money for it before the end of the water heater's life. We finally decided after much debate that we just couldn't afford to put in a tankless at this time, and that as much hot water as we use for our family of five, that this would not be the best choice for us anyway. Finally one day, while I was at the very end of a long drive home from visiting my Dad and almost home, I got a frantic call from Tommy. He was shouting into the phone "How do you turn off the $%&*^$%^$*& WATER!! It's everywhere! I can't get it to stop!"
I put my foot to the floor and got home in record time and by this time he had found the shutuff, and was mopping up a big mess in my laundry room.
I called around, of course you KNOW it was a weekend and plumbers were charging a premium. I had one estimate of 1200 dollars to replace the one we had with one exactly like it. Thinking this was a little pricey I called Home Depot, ordered one over the phone and they delivered and installed it the next day. The whole thing only cost me six hundred dollars and I have not had a water heater worry since that day.