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I mainly use the back brake.
I therefore propose option 4: improve your braking technique before spending any money.
If you only use half of your bicycle's brakes, you can't expect to stop quickly. Further, you're using much less than half your available braking force, because the back brake is much less effective than the front one. This is because, as you brake, your weight shifts forwards, pushing your front wheel harder onto the ground and reducing your weight on the back wheel. On a dry road, your front brake can do almost all the work of stopping you, and stop you much faster than your rear brake. On a wet road, you need to make more careful use of both brakes because of the decreased grip of your tyres but, still, you need to be using the front brake much more than you do.
Sheldon Brown, as always, has lots of advice on braking. Many people worry that using the front brake will cause you to go over the handlebars. It is true that if you screw up really badly and front-brake really, very, a lot, much too hard, you might go over the handlebars. I have never come close to doing this. In fifteen years of commuting by bike in two of the UK's biggest cycling cities, I've never seen anybody else do it, either. It's an incredibly rare thing to happen and not something you should be afraid of.
The main difference from rear-wheel braking is that you can essentially pull the rear brake as hard as you like and the worst that can happen is that your rear wheel will skid, which you can stop by letting go of the brakes for a moment. To use the front brake, you do need to learn how hard you can pull it in different situations. As with everything about riding bikes, the way to learn is to practise on a quiet road. I categorically promise to you that, if you brake gently with the front brake, you will not go over the handlebars. You can then experiment by braking a bit harder and moving a bit faster. You'll find that you can brake pretty hard without coming even close to having something bad happen. Brace your arms against the handlebars, too, so you're not lungeing forwards faster than the bike as you stop.
A couple of other things to bear in mind when braking in the wet.
Manhole covers and painted lines in the road can be extremely slippery: avoid them where possible. This is particularly important when using the front brake because front-wheel skids are harder to recover from; it's also important while cornering.
In general, even in the dry, be wary of using the front brake while cornering since a skid is more likely when you're putting load on the tyre by cornering and braking at the same time.
If you see that you might need to brake soon, gently apply the brakes to remove some of the water from the wheel rims. Then, if you do need to brake, your brakes will be more effective.