Sorry, wasn't implying that you should have to know if the designers made good choices, really meant that you have to look at the bike as a whole, not just at the material used for one of many parts. These bikes are made by Giant, a company that makes good bikes for their own brand and manufacturers bikes for other well known brands. Giant has been making aluminum frames for a very long time, they know what they are doing. Heck, I have a entry level Giant commuter bike with an Al frame and no suspension and I love it. It's perfect for what I do (riding around for fun and to run quick errands on pavement), which is very similar to what you want to do. The thought that the aluminum was delivering a harsh ride has never once crossed my mind. As for your question about the suspension forks, I don't think are on those bikes because of the alum frame, I think they're on those bikes for marketing purposes.
Don't over think and over research this, just go to the other shop and test ride them.