For under 25000 RS, HTC and Samsung are going to be your best choice along with Sony, Motorola, LG and other Android manufacturers.
First of all, I'll explain about hardware and software and everything you need to know:
I really prefer Android. For starters, using Android is like being an admin, using other operating systems (iOS, Blackberry) is like being only a user. You can do much more on Android than other systems. Such as changing your keyboard, it's amazing as you don't get controled by the system what you do. You control it.
It's like being the boss of a company and being just a worker. You have that choice thing: what keyboard, what lockscreen, what browser, what email client, what launcher, what operating system even. Believe or not: if you have Android, you can replace it with another operating system. This is called installing a custom ROM. You also have more hardware flexibility as well. Real hard keyboard or a pretend one? How big? How wide? How thin? How expensive? Again, you have that choice thing.
For internal memory, this is how much you get. Most phones have a choice how much you want. 8GB, 16GB 32GB or 64GB. This is how much you have to store things like photos, songs, ebooks, files, apps, etc. A 64GB would represent a whole library whilst an 8GB is only one shelf. Very simple. More space is more expensive. If you work a lot and always installing and downloading things, then I recommend a 32GB or perhaps 64GB. If you don't use your phone that much, just an 8GB would do fine actually.
RAM is similar but yet different. RAM stands for "Random Access Memory". If you like to have lots of tabs and apps and songs and software opened at the same time, you will require a bigger RAM. There's a 512MB, 1GB, 2GB and very lately, the Samsung Galaxy Note 3 and LG Optimus G2 has a 3GB RAM. You don't really need a large RAM but of course, a bigger RAM will have a faster speed. But if you close your tabs and apps frequently then you only need a 1GB RAM, perhaps less.
Processor is measured in cores and GHz. Single Core is the slowest, then Dual Core, and Quad Core is the fastest. GHz is quite simple. The bigger the number, the faster. So a 2.3GHz would be faster than a 1.4GHz. To be honest, some phone models are a bit over. You don't need 1.5GHz+.
Longer battery is also faster. Another alternative to getting a long-battery phone is to get a phone with swappable phone. You could literally get the battery out and put another battery in.
Durability goes to Sony and HTC. Great build and some of their models are waterproof (please check for sure it's waterproof before bringing it into the shower with you!)
Overall, here are the phones I suggest you pay attention to which meet your price requirements plus have decent quality (software and hardware):
Samsung Galaxy Core
Samsung Galaxy Win
Samsung Galaxy S4 mini
Samsung Galaxy Grand
HTC One mini
HTC One V
HTC One X
HTC Evo 3D
LG Optimus F7
LG Optimus L5
LG Optimus G
LG Google Nexus 5
Huawei Ascend Y300
Sony Xperia V
Sony Xperia J
Sony Xperia M
Motorola Moto G
I suggest going to phone/electronics shop such as Best Buy/Power Mall/Jaymart. Doesn't really matter, as long as they have the phone you have. Try it! Compare them to other phones you can afford. The phones I suggested are all Android.
In case you want Windows or something else, here's some recommendations:
Nokia Lumia 520
Nokia Lumia 620
Nokia Lumia 720
HTC 8X
Samsung Ativ S