Doran’s Blade + pot – You need AD, you need health, you need lifesteal – Good for ADC starts. Pretty much the default ADC starting buy.
Longsword + more pots – A more sustained start, but lacking sustain a little later until you get that rushed vamp scepter. Considered a more defensive ADC start. You lose a little bit of health and a little bit of farming power early, but get into your build faster. Riskier, but more rewarding.
Brawler’s Glove + pots – For rushing static shiv. A good start for a split pusher, not so great for early farm or sustain though. If you pick this start, you’re going to lose early but will likely take a tower before your enemy later. Good build for punishing a crap early game champ like Vayne. Also, that small chance of an early crit can win you a trade under the right odds.
Boots + pots – Good for dodging heavy skill shots or versus an early ganking jungler like xin zhao. Also a non-build punishing start like long sword. Dorans items are a gold loss. A good and reliable gold loss, but still a gold loss.
Null magic + pots – Good on Galio, also good if you know the enemy laner is going to attempt to crush you with AP. You’re gonna start hurting pretty bad in farm and damage, but the good news is you aren’t gonna snowball the enemy APC if you play smart. Build it into merc treads. Good start versus fizz, akali, kat, etc. This is a default build path for a Yasuo into Annie, Akali, etc. That’s the type of situation that would warrant this.
Sapphire Crystal + pots – Good for mana hungry champs, mana scaling champs, or anyone that has mana issues and rushes trinity force or a sheen item.
Ruby Crystal + pots – Good for health scaling champs that are facing a punishing lane or rushing trinity force. Great for a support that wants to rush sightstone.
boost pot + pots (red or blue boost) – Good for an early all-in and securing an early advantage. But if you manage to whiff your early trade, its a huge gold waste. Quick pro-tip – Do not do this on Akali or Zed. If you build a red or blue pot on Akali or Zed expecting to snowball, you’re an idiot. They can’t snowball until 6, period. Katarina or Fizz maybe, but not the other two.
Flask + pots – Use for resource intensive champs who are weak until 6 or on mana hungry champs that need to spam spells but won’t get a good mana pool until later. (like Talon or Elise).
Doran’s ring + pots – Good for most AP mids. Mana, mana regen, health… what more could you ask for? There aren’t many APC champs that don’t start this way.
Doran’s shield + pots – Good for heavy auto attack matchups. Also good for champs that want to start tanky and build health (like mundo or vlad, though some argue that ruby is a better start for tanky health scaling/health pool champs)
Cloth armor + pots – Good against a heavy AD lane when playing a bit of a squishy. Especially if they can build it viably into seeker’s armguard and eventually zhonyas.
Rejuvenation Bead + pots – A good start for a tanky laner who knows he’s not gonna get beat on too hard, or if they’re rushing Tiamat and need more early sustain than early damage (long sword instead). Also, you see this on Vlad a lot.
A mix of pots and wards – Good for a high pressure, high damage support like Annie who can probably get an early assist or kill to purchase her gold item with a little later than usual. Makes for a very secure lane against early ganks
Dagger+pots – Good for champs that have life replenish or on hit effects like xin, diana, or irelia
Double faerie charm and mana pots – For the mana hungry as all holy getout champions who need all the mana they can possibly get in the early game and are rushing into a chalice or idol. Not much of a DPS loss over a doran’s ring, considering the vast increase in spellcast potential and the rush into athene’s.
Machete+pots – If you’re jungling. Derp.
Amp tome – Good for AP champs that don’t use mana and need that extra “umph” when arriving in lane, and great for rushing a haunting guise or hextech.
Spellthief + pots – Good for caster supports and it’s the only mana regen support item that gives you GP10 right off the bat. Talisman requires the 2nd tier before you get your GP10. This item is better for caster supports that need to actually get some AP together, like Lux or Morgana.
Ancient coin + Pots – Good for utility casters as the mana/health regen is higher and talisman of ascension is 100% core on any utility caster. Works great with Orianna support because she can speed a tank up with a ball on their head for even more speed and cast Shockwave once they get in range of an engage. Works great with Evelynn’s R/E combo too. Sometimes works on tanks, too. I’ve used it on Leona with some success.
Relic Shield + Pots – Good for melee or tank supports for a sustained and safe lane. Or if you want a heal on somebody that doesn’t inherently have one. Really shines if you build a lot of health and a locket/Mikaels alongside it.