1. Waterproof / Weatherproof
If you're after a waterproof truck bed cover, it's important to mention that nearly no tonneau cover can keep out all of the rain and moisture outside, but a few get close. Solid one-piece covers are arguably the most waterproof since they're not meant to be taken off frequently and can't be split into multiple sections to only open a portion of the truck, hence eliminating a possible weak point where the water can enter.
Hard tops are always more weatherproof than their soft-top counterparts, whether we're talking about folding, retractable or roll-up covers. Soft tops are also more susceptible to damage from the elements in the long run, so if you want a cover that will last you a long time and waterproofing is at the very top of your list, choose a hard top or a solid one-piece cover.
2. Security
Again, much like with waterproofing, hard tops are better if security is at the top of your list for the very same reasons. Hard tops can't be sliced through with a knife or another sharp object as easily as soft tops can, though they're still slightly worse than solid one-piece covers which reign supreme when it comes to security. If you're interested in locking truck bed covers, your best bet is either a solid one-piece cover or any of the hard tops which feature a locking mechanism.
3. Level of Install Difficulty
When it comes to ease of installation, soft tops are noticeably better in this department because they weigh less due to their fabric constriction, making them easier to align and mount. You can install most soft tops on your own, but you'll almost certainly need a friend or two to help out when installing a hard top. Solid one-piece covers are the most difficult to install and require the most amount of labor, but that's the cost you pay for the added security.
4. Ease of Access
Retractable tonneau covers are the easiest to open, which makes sense since that's what they were primarily designed for. Foldable covers are a close second, especially because you can only fold a single portion of the bed and get everything you need super quickly. Roll-up covers are also easy to open, but they're slightly more tedious since you have to manually roll up the cover yourself. Hard tops are always more restrictive than soft tops because they're less flexible, weigh more, and therefore take longer to open or fold.
5. Durability
Hard tops are almost always more durable than their soft top counterparts simply because of the material they're made from. Soft tops are constructed from vinyl or fabric, making them susceptible to damage from the elements such as color degradation from the sun or ripples caused by water and snow. As time goes on, the fabric/vinyl can become wrinkly and stretched out, whereas a hard top cover will always remain the same structurally, apart from maybe some color degradation or flaking caused by the sun.
6. Budget
This is a tricky one to answer since the cost of a tonneau cover will vary greatly depending on the make and model of your vehicle, as well as the tonneau cover manufacturer and product.