Recommendation for carpet padding?

Hello,

I need to select a carpet pad soon and I value the Board's input. Here's what I have to select from:

1. 1/2" pad. Nice, thick and comfortable to walk on. Reasonably priced.

2. A bit thinner, denser, with a water barrier protection that is 40 cents more a square foot. So now I'm looking at another $500 on top of the $1,020 that I'm paying now.

Here's my situation:

1. Berber-type carpeting.

2. Radiant heat in floor doesn't work. (I have valance style radiant. Works wonderfully.)

3. No kids, no pets. So no spilt drinks.

4. Carpet will be installed in the three bedrooms, hallway that connects all three bedrooms and the living room. Not in the entry way, kitchen or dining room.

5. I have linoleum tile (the asbestos laden kind) in the bedrooms. They'll stay where they are. I don't see any evidence of seepage or moisture.

I sorta like the thicker pad, but who knows.....

Please let me know.

thanks.

David