My project is to turn my Alero into more of a lowrider than a racing car. I'm looking for a smooth ride. I'm thinking the Eibach springs seem like my best choice but I'm open to suggestions.

For smoothness, Eibach is your best bet. It's as close to stock as you are going to get. I'm more into the agressive looks that the Intraxs offer, so I'm probably going to get those once I complete my stereo setup.

and how easy are they to install?

Easy if you have some basic tools, some jackstands, and a friend to help you. I know a shop that will do it for me for $50, so I'm gonna have them do mine once I get the money.

You really need air tools to do them yourselves, or else it will be pretty difficult.

I think the general concensus is this:

For track, Eibach is the best because they are a progressive spring.

For everyday driving & good drop, Intrax is the best because the ride is very nice, and the drop is also very nice.

For lowering, ST (Springtech) springs are the best, because they are the lowest (although it hasn't been proven).

^Would it matter what type of suspension package you have as to which springs would work best? I have the Sport Suspension. Not planning on racing her at the track for at least another 30-40k miles but then after that who knows?