I'm looking at getting a road bike. I have to say I'm interested primarily for recreation/exercise. However, I'm not interested in casual touring around town. I would like to break a sweat. On the otherhand, although I wouldn't mind going fast, being the fastest on the block isn't my goal either.

That said I'm trying to find an entry level road bike and for all my looking and reading, I'm only slowly getting smarter on the subject. For instance, the only thing I've decided on so far is that I want to be above sora level components because I don't want to lock myself out of an upgrade path. When I look at bikes that fit that description, I roughly get things around my price point too.

Anyway, the next thing that's got me puzzled are the fact I see bike frame geometries come in basically two flavors. Essentially flat top tubes and sloping top tubes.
Here are some bikes that show the difference:
https://www.trekbikes.com/bikes/2005/road/1200.jsp
https://www.trekbikes.com/bikes/2005/road/1200c.jsp

I figure the higher handlebars give you a more upright (comfortable) position in the example of the 1200C. But is that all that's going on with the sloping top tube frames?

Based on what I described above as my interest, which one is better suited for me?

Can I add a stem with an adjustable rise and give myself some degree of flexibility between the two styles?

[edit] spelling.

Level or sloping toptube makes no difference,except sloping sometimes works better for people with short inseams and longer torsos. Buy the one that fits you best. Who knows if a drop or flat bar will work best for you. Everyone usually ends up with an ultimate preference,but you may not know what it is starting off.

best thing to do is go to your lbs and ride both as there is no general preference for everyone. whichever one is more comfortable for you is obviously your pick.
also like sydney mentioned you might want to compare drop bar road bikes to flat bar road bikes as well.

If you want to go fast and break out into a sweat, skip the hybrid-looking 1200C. Go for a real road bike. Something that looks like the 1200.
But don't settle on Trek necessarily. Look at other brands, test ride them, and get the one you like.

Get the drop bars.

You don't have to ride in the low part.

The difference you have shown is the difference between the "traditional" frame and the new "compact" frame. The compact frame has a smaller frame hence the sloping top tube. The idea is that a smaller frame is lighter. But the problem is that you need a much longer and stiffer seat post. Any weight savings are apparantly lost when you add in the seat post. So it seems that the compact frames are an improvement that isn't. However, if you like the looks of the compact frames, by all reports, they are perfectly good bikes.

The incline in the toptube increases torsional stiffness. The seat flexing over and out of alingnment with the bb.