hi guys
i am really a total newbie when it comes about bitcoin mining. i've read here and there about mining bitcoin with Sha or mining other crypto currencies with Scrypt, but still i am not sure which one is better and i am not sure if it is smart to get into the mining now?
i understood that the difficulty increases and that the main factors are:
1. the price of the mining unit (the miner)
2. the difficulty level
3. the price per electricity (kw/s)
4. and what else? to be honest i do not know too much now and i will be really grateful if anyone would be kind enough to advise me to buy a miner or not? and if yes - should it be Sha256 or Scrypt miner?
if someone have some time to drop a link or an explanation which shows how the difficulty "should" increase in future i will be thankful too.

by the way - what is the best place to buy a script or sha miner? china? some website?

thank you all!