From my experience at ~30 hours and having flown a '99 172R, '03 172SP and a '98 Archer PA-28-181, I can give some general answers:
The 172 is a little more responsive on the controls. The Archer, like my CFI describes, flies like a Cadillac. It's super smooth (not that the 172 isn't) and requires smoother inputs. The Archer really enjoys being trimmed for level flight and the 172 is a little more forgiving in this aspect. One thing I like about the Archer is that the nosewheel has a direct connection to your rudder pedals. This makes taxiing a breeze. The 172 has bungees on the nosewheel. If they are worn out, you have to sort of anticipate the turn and use more differential braking.
The 172 and the Archer have different landing characteristics. You need to come in faster in the Archer and really be smooth on the touchdown. The Archer has a noticeable ground effect, but it goes away quickly. My CFI explained many pilots have a tendency to let the Archer slam into the ground because they are too high above the runway letting the ground effect bleed off. It can be hard to gauge where the wheels are in the Archer because you can't see them. The 172 is easy to land and is predictable in that matter.
If you really like looking straight down while in the air, the 172 is the way to go. I rather enjoy the view in the Archer. You can't look straight down, but you can see up into the sky and around on the ground. It was refreshing after flying the 172, since the 172 is kinda like wearing a baseball cap.
Personally, I found the Archer to be super comfortable in comparison to the 172. The 172 sits like a Ford Ranger while the Archer sits like my BMW. It's not like the 172 isn't comfortable. I just felt like I have more room and a better seating position in the Archer. Plus, this particular Archer I flew has some sweet seats. I'm actually trying to get myself checked out in the Archer so I can take it on a XC simply for comfort. However, the Archer burns way more gas than the XC and isn't all that much faster, so it isn't necessarily the better choice.
Most people start in the 172. I would fly that around and then once you are comfortable with flying, you should ask your CFI if you can take an Archer (or whatever you have access to) out for a flight. That's what I did.