Triple panes do more to mitigate sound than heat, you have SOME benefit to going with the extra pane, but the expense consideration is important. You need to ask yourself a few questions: 1. How long are you going to live in this home? 2. How much more expensive is the triple pane glass unit? (x number of windows) 3. How much money do you really anticipate saving in heating/cooling costs over the period of time you expect to be there? 4. Understand that potential home buyers are NOT going to consider triple pane windows in their buying decision, but they WILL care if they are single panes...
My guess is that the cost benefit analysis will show that the double panes are a better investment, and use the money you save for some really good window coverings.
As far as insulated frames are concerned, understand that the surface area of the frame, compared to the surface area of the window itself, makes this "issue" highly irrelevant. Even a poorly insulated frame is still not an issue compared to the heat loss through a double or even triple pane unit.
The most important factor I look at in windows are ease of use, reliable hardware, ease of maintenance, and a company that will be around long enough to back up their warranty. (most window warranties are for 20 years, but good ONLY to the ORIGINAL PURCHASER. If you have a sealed window unit fail, make sure you replace it BEFORE you sell the house. It should be at no cost to you.)