Borderlands Rack Hive

In short, the answer is "no."

In long, there are actually a handful of things you can evaluate.

First of all, money is a terrible indicator. It tells you nothing. I've had weapons worth a 10th as much as others that were OBVIOUSLY better. I think money is calculated based on part levels and rarity, but those often mean quite little in the latter part of the game.

While it seems like it can be easy to calculate DPS of weapons, it can often be hard as reload speed can often factor in quite a bit. For example, I once had a weapon with only a two round magazine with a high damage and wanted to compare it to a weapon with a slighter lower damage output but a much larger clip. Well, since I was playing a hunter, I had lots of points put into my pistol re-load speed, so it made it really hard to figure it out.

What I did then, was fire each of them continuously for a set period of time (say 20 seconds) and count the number of times each of them fires. This then factors in your reload speed as well. Then, simply figure out how much damage each shot does (multiplying for shotguns if necessary) then divide by time. I determined that even though I was reloading VERY frequently with the smaller magazine revolver, it's damage output was a full 33% higher than the other gun.

While this strategy works great for guns without elemental effects, it's a lot more challenging when it comes time to compare elemental damages. As a basic rule of thumb, compare apples to apples, i.e. compare fire to fire and so forth. x4 beats x3, etc, so that's often easy to figure out. You also generally want to try to have at least a fire and a corrosive gun on you at all times, and hopefully an electricity gun at all time. So when you are comparing, compare specific elemental slots to each other.

There are a few factors that you can't count for, such as zoom factor. Some people like zoom, other don't. It's worth something different to everyone, so give it as much weight as you want. Magazine size, bullet count, and damage can all be used to calculate overall DPS as I listed above.

Finally, learn what the special effects on the rare weapons do. There's a great list here:

http://borderlands.wikia.com/wiki/Special_Weapon_Effects

Some of the effects are pointless, only affecting things like the spread of the bullets, meaning that you could easily find a purple or even a blue better than said orange. Other effects significantly increase the damage of the element or something similar, so be sure you know what you have.

There's nothing clear cut, but you can do pretty well most of the time. Finally, there's no accounting for tastes/real world experience. If you can't decide which is better, carry both for a while and see which one feels most awesome. Use that one.

Edit

Well since people are actually reading this, there's a little bit more information on each point.

The answers in order:

• Yes - All quests reset - The game begins just as though you had started at lvl 1 (minus the character selection, so you'll have to do everything over again (including the tutorial!)
• No - You keep everything - This is pretty straightforward, what you have on you at the end of playthrough 1 stays with you. However, items in playthrough 2 are scaled (see below on scaling). So you'll find the same named weapons but they will have better stats, so don't just ignore them.
• Yes - Mobs scale to your level -It is expected that after completing your first playthrough you will be around lvl 35 (give or take). Therefore when you start a new game, the mobs will have 35 added to their level (again give or take a level). Which is why specific enemies (like Crawmerax for example) have a set level. If you're looking to do the Secret Armory of General Knoxx, you should be lvl 50ish (about 2.5 playthroughs).
• No - You can go find it in playthrough 2, or you can access playthrough one with your current character (so if you have gained a level in playthrough 2, that level sticks when going back to playthrough 1). This includes any subsequent playthroughs.

Hope that helps!