Okay, let me give a deeper analysis.
If you want to do a dedicated workout on the bike (i.e. 60-120 minute rides), get a road bike. Don't bother with hybrid, it's pointless and mostly unergonomic. The riding position on a road bike can't be matched, even though it may look less comfortable at first glance. Uprightness gives you less control at speed, worse braking, etc. It's a bad idea.
If you want to ride more upright, add a spacer to the steering tube of a road bike.
If you plan on riding both on-road and off-road, a cyclocross bike will give the best experience, unless you plan on doing big jumps or rocky/sandy trails. The latter require a mountain bike for the wider tire that can cope better with rutted or very soft surfaces, as well as the suspension to deal with harsh bumps.
BUT! If you want to get the bike to...you know... get to the gym, then this is the type of bike you should get, and you should not pay more than 300 dollars on it:
And anyone telling you anything else has no idea what they're talking about.
For any ride shorter than 15 miles, that is all the bike you'll ever need, it will work off-road, it will work onroad, you'll be upright and relaxed, and you'll have something to get out of the shed for when getting into the car seems pointless, and going by foot seems exaggerated.
From my experience, it doesn't matter what a bike looks like, with regard to how likely it is to get stolen. In fact, old cheap bikes are far more likely to disappear, than are relatively new ones, mostly because they're an easier sale on Craigslist, compared to something that should be going for a few kilobucks, but has to be sold at a price that makes it sell quick, and thus makes it appear fishy. People are also more likely to check expensive bikes for telltale sings of stolen goods.
A set of good locks, and intelligent bike storage will massively increase the probability that your bike will still be where you left it.