Are 2 Doran Blades a more viable item buy than Berserker Greaves/just saving up for a BF Sword early game?
Doran's items are excellent for early game.
When you should buy ?
- If you are having a slow or bad early game.
When you should stop buying ?
If you start your game with a good advantage (let's say 3-0-0 before 5min or any other great start set), you can skip the Doran's itens and go for others like Brutalizer or even BF Sword.
When you get 2 some times 3 (but this is kind rare), you should stop buying them, because the game will probably be going to mid, and switch lane phases.
Should I store money until I get gold enough to buy BF sword, instead of Doran`s ?
No, If you do not buy items, to scale with your level, you will be too much week (works as when you are being too much harass that you can't farm at all. So you do no damage in few minutes)
The answer is "It depends".
Your first major purchase as an AD carry should be BF Sword. Sometimes circumstances don't let you farm as much as you would like and you are forced to return to base earlier than you would like. Let's look at the following scenarios (all assume Doran's Blade is first purchase at the start of the game, though this is not required):
If you have a healer in lane I would recommending skipping the second Doran's Blade in favor of +1 Boots. The extra move speed will get you out of a number of sticky situations and increase your survivability as a result. They also help dodge a lot more harass than you might expect. As the AD carry you don't really WANT to be taking the damage and as a result, the benefit of having +100 hit-points can be outweighed by being in a better position (boots can help you get there). Also, the healer should be keeping you as topped off as possible.
If you DO NOT have a healer in lane, the argument for a second Doran's Blade becomes much stronger. Since you are relying on your passive regeneration, potions and life-steal to keep you in lane every individual hit-point you have at your disposal becomes more important.
Another option if you find you are getting ganked too often is to pick up a sight ward. 75g for the peace of mind that the enemy isn't waiting in that bush in river is worth it in most cases. This applies whether or not your support is buying wards already. Wards win games, don't believe anyone who tells you otherwise.
When laning with a partner you trust (someone you play with regularly who understands the support role) you may even want to consider dropping the first Doran's purchase for +1 Boots and 3 Potions. That translates to 600 hps of sustaining power through potions and the maneuverability to dodge harass if you can see it coming. Also, the bonus damage in the laning phase (before your BF Sword purchase) is mostly last hit damage and can be compensated for by paying close attention to minion health rather than purchasing +10 damage that doesn't build into a late game item you want.
One or more Doran's Blades are typically purchased by botlane AD carries for the purpose of adding durability while still increasing damage output. Beyond that, they are also very cost-effective, granting more stats than the amount of gold invested "should" due to the fact that they do not build into anything.
It mostly depends on your farming capabilities and how soon you return to shop. If you are getting harassed and are forced to return to shop early then its not a bad idea to grab a second dorans for some damage so you don't head out there empty handed. But if you get back to shop and you have enough for the BF sword then I would reccomened you purchase that. The percentage of lifesteal will increase greatly from your first dorans and the 100 health really isn't that great unless your lane partner is horrible.
Personally I do my best to stay in lane until I have farmed enough for the BF sword AND my tier one boots, but if I get forced back I will settle for the second blade and the boots.
Also, I would almost always make sure you are getting some hefty damage output before you finish off your boots. Tier one boot swill suffice until you can get that BF sword.