which do you prefer and why?

upgraded boots and double dorans blade

-or-

bf sword

Upgraded boots and double dorans cause movement speed is really important. Also, upgraded boots gives you benefits other than ad whic is crucial. Of course, you're talking about early game right?

yes, i'm talking about 8-9 min into the game when u have about 1600 gold if you're good at last hitting and maybe picked up a kill. The only problem I have with going upgraded boots and double dorans blade is that it almost forces you to go for trinity as your next item if your playing a carry like ezreal or corki. I think its much more effective to go with a rushed blood thirster which can be acquired by about 13 min.

It depends. Are you getting harassed a lot and require that security you get from the health, lifesteal & movespeed from those items? or are you destroying them and want to destroy them faster?

If I have, say, soraka or taric healing me a bunch, I don't need to worry too much about the extra health. Also if they aren't harassing me a lot and I don't really need the lifesteal, then that works well too. The main thing is that with dorans, you have to sell them, so they're meant more for security in lane rather than just a core item as they don't build into anything.

You could, in essence, reach your safest point faster if you go bf sword first (you could get a really quick bloodthirster which is more damage and lifesteal than 2 dorans blades will ever hope to achieve.) The way I view it is this.

BF-Sword first: Weak -> Weak -> Very Strong
Dorans: Weak -> Not so weak -> Somewhat strong -> Very Strong

So, it's your pick. If you're doing well and can afford to go without, then do it immediately, otherwise, just go for the dorans. If you're questioning whether or not you should go for either dorans or bf sword, go dorans, because dorans are never a bad idea.

2x Doran's Blade + Upgraded boots is way better.

Of course, if you're running Ezreal/Corki, I'd probably just get a Phage and either rush Trinity or go BT --> Trinity.

It all depends on the lanes.

If your afraid of getting bursted down. (Sona, Taric, Graves, Maybe even Ez)
-Double Dorans
or
-phage

If your the one doing the bursting
-BF sword
-dorans
-sheen(maybe)

Basically my rule is, buy dorans until your tanky enough, normally 1 is enough for me on graves, 2 on nearly anyone else, if its a slow game. And as someone who plays AD a lot. Finishing boots on any of the top 3 AD's (Graves, Ez, Corki) Should not occur in my mind until either you plan on leaving lane. Or you already have your BF sword. **** if lane goes well I have BT or IE before I finish boots. Just because the MS boost doesnt do much for you in lane, compared to a dorans or vamp scepter or bigger item. And the percentage AS boost doesnt do much until you get Zeal at least.