"Best" is subjective.
The different choices of baking pans will effect texture and baking time. The more surface area the more crust and the faster the baking time.
Recipes call for a bread pan simply because then it looks like bread and is easier to slice. As you noticed, it does require longer to bake.
Muffin pans are also very popular because of the convenient shape and faster baking time.
If you like the shape and texture of your bread in a baking dish then by all means keep using it. I won't criticize you for it.
Removing things from the oven halfway through is not very friendly to baked goods. In general, they'll collapse as they cool off since the structure isn't cooked and set, and the leavening (baking soda/powder in these cases) will be spent, so there's no way to get what you originally wanted. It might be something like what'd happen if you forgot the leavening in the first place.
In general: if there's only 5-15 minutes left, just leave it in, and the heat retained by the oven will take care of things. If it's barely started - just beginning to get warm, not bubbling/rising much - probably best to take it out and wait to bake later, especially if it's something that can survive waiting at room temperature. Anything else, leave it in and hope the power comes back; it's going to be ruined if you take it out and ruined if the power doesn't come back on so you might as well go for it.
So for example, cookies could probably survive this by leaving them in. They don't have very long baking times - somewhere in the 5-15 minute range. Your oven won't cool off all that much in that time without power. So if you leave them in for a little bit longer than the original baking time, they'll probably be fine. If your oven has a window, look in with a flashlight to check on them - you don't want to open it to check them.
A cake is iffier. If it's 15 minutes into a 45 minute baking time, you may just be out of luck. I think I'd still leave it in, hoping that the power comes back within 5-10 minutes, in which case it'd probably make it. As I mentioned earlier, if you lose power early and for long enough, the cake will have spent its leavening and collapsed. You could finish baking it, but it'll still be collapsed - it probably won't have a terribly palatable texture (definitely dense, maybe chewy).
The only time this has actually happened to me was with some cornbread muffins, around 2/3 of the way through their baking time, and the oven didn't have a window. I wildly guessed how much extra time to add, pulled them out then, and they were great. So there is hope!
Best Answer
It's never the best of an idea taking the cake out of the oven during its cooking as you'll probably knock it a bit and knock the air out and then it'll cool down a bit and so take longer too cook. Saying that, the whole thing is when you take the cake out. As a rule don't take your cake out until at least half-way through the cooking time, that way the starch will have started to set. If you take your cake out multiple times 5 minutes before, say, it don't make to much of a difference as by then the cake is practically cooked.
Some cakes are more susceptible: foam cakes (genoise, chiffon, etc) are the most likely to feel the full force of you taking the cake out of the oven as it will likely deflate all of the air you've worked so hard to create, however, butter cakes (pound, fruit, etc) wil not be so effected as these are a lot denser and rely more on chemical leaveners.
There are lots of ways to check if your cakes done. If its a cake with quite a thin batter, open the oven door and give it a tiny wobble (not a great big shake to deflate it) and if it wobbles its definitely not done, if it doesn't wobble you can progress to the next step which is poking in a skewer or knife and if it comes out clean it's done, use this technique for all cake types. Another way is when the cake looks golden (unless it's a chocolate cake), press your finger down on the cake and if it springs back it's done. A lot is made about not opening your oven door, in modern ovens today, this doesn't make much of a difference as they can quickly get back up to temperature, particularly if you just open the door a crack. On a final point having a reliable oven temperature is one of the most important steps. Buying a little oven thermometer is a good investment, they're very cheap and will save a lot of hastle