I am not an expert in this particular area but I can share some personal experiences with you.
It seems as though the general consensus is that Electric Hot Water heating is the most expensive. Then, depending on the area of the country you live, next might be Oil Hot Water, then Gas How Water, then Gas Forced Air. In my part of the country, Mid-Atlantic, this is basically the order (and you may have a variation here and there in my area). Anyway, I prefer Forced Hot Air. Why? I won't experience noisy pipes (potentially or otherwise), water leaks, A/C is part of the system along with a Humidifier, and it's pretty cheap. For a 2-story 4 bedroom Colonial with a wife and 1 child, I pay about $40 per month for heat, hot water, AND stove. That's just the Natural Gas portion of the utility bill. With this type of system, if you want to add a room or a 'vent' somewhere, you've got to be able to run duct to the vent, and deal with the possibly of return-air. Now, in order to adequately determine if you can put in A/C in your prospective home, I'd see about paying a contractor his 'show-up' fee to come to the house of your dreams and give you an estimate. That's a pretty cheap price to pay knowing BEFORE YOU SIGN A P&S AGREEMENT that you can do what you want. Not much to pay when you're willing to spend $100,000 (or whatever) for a home you'll be paying on for years and years. On a side note, riends of ours have a split level with baseboard hot water heat and they put in A/C. The duct work was limited to the crawl space area for the most part but the home is centrally-cooled. It cast about $2500! Certainly the installation was not done in the same way had it been done when the home was first built. Their 1st floor and lower level are on concrete slabs so running ducts to, say, the 'other side of a room' was out of the question. On another side note, when my wife and I went to buy our 1st home, we sat down and WROTE down what we wanted in a home. I wanted everything Natural Gas, an unfinished basement, a large yard, etc.. She wanted a Family Room, a 1st floor bathroom, Central A/C (see? A/C alreay installed), etc., etc.. Again, that 'show-up' fee is cheap!
Now, about hot water heat. I'll skip the Oil, Electric, Natural Gas thing ... You already know what I don't like about this particular type of system (and it's only my opinion). What I DO like about it is its relative ease to do zone heating! I can't say much about 'ease' in older homes but in newer ones I don't think it's too bad. (I'm hoping someone else can give you more on this. I could be completely wrong.) I don't know how efficient hot water heat is but my guess is it's not 'too' efficient. Insulating pipes, like duct work, is one way to mitigate your 'loses'.
Good luck. I hope your house hunting goes well. I'd call that contractor out to estimate the cost of installing A/C if it's not already in the home when you find that home of your dreams, and MAKE SURE this 'item' goes on your P&S Agreement as a 'condition' for your purchase (in that you feel that if the cost to put A/C in the house is affordable to you, you'll buy the house.) Just for trivia, you can put almost any condition-of-sale, within reason, in a P&S Agreement.