Spellsword is available a tiny bit earlier than Sorrowblade, so it might be better in some very narrow circumstances. If a player happens to be 200 gold short of Sorrowblade and they need to gank someone immediately then it might be a good choice. I ran into just that situation last night, where we had Anka against an enemy SAW, and I was passing by the store on the way to help, and I could afford Spellsword right then or I could wait for 200 more gold to buy Sorrowblade; I bought the Spellsword, and Anka and I quickly assainated all three enemy laners starting with SAW.
I was wondering just how narrow that gap is between when you can get the items out, so I just ran a bunch of bot matches to see just how quickly I can farm certain items. I followed the same path each time, teleported to buy the Heavy Blade and Prism (which did little to my total time, since it happened when I would be going to restart my circuit anyway), and avoided killing any bots. It’s not totally scientific, because I got some ambient as I passed through lanes, and in a real match I’d need to fight players a bit (which might give me much more or much less gold) but the broad strokes were pretty clear.
I bought Spellsword at level 6 at 6:40.
I bought Sorrowblade at level 6 at 7:02.
I bought Shatterglass at level 6 at 6:59.
I bought a Stormcrown at level 5 at 4:30. To be sure it wasn’t a fluke, I did it again, and it was in my inventory at the same time, give or take a second.
I started with a Stormguard Banner but built Sorrowblade at 7:17. I could have gotten it out sooner if I sold the banner, but I didn’t think that far ahead.
I didn’t mean to make it part of the tests, but I used A+B to stun and run from bots in each one. I hit different bots each time, so I don’t know precise damage numbers, but getting hit with Stormguard Banner, Heavy Blade, or Heavy Prism while you’re level 4 would be a significant emotional event. If I had to pick, I’d say Stormguard was a bit more damage, but with any of them the victim could probably run to safety.
The Sorrowblade build felt like it cleared faster than the Shatterglass build, but the tests really didn’t show it. 2 Crystal Bits was slower than 2 Weapon Blades, but once I got a heavy item in each build, CP picked up speed. Mostly, the speed worked out the same because WP was not so much faster that it let me clear extra camps (like Stormguard Banner did), so I was more limited by my jungle rotation than by damage.
When I play the Stormcrown build to 7 minutes, I can buy a Heavy Blade or Heavy Prism, so the damage output is still more than with Sorrowblade or Shatterglass at that point.
I’m not sure about Stormcrown, but the Stormguard Banner is unquestionably the best item to start with for any build for two reasons. First, it’s revenue neutral — it helps your farming efficiency enough to pay for itself by the time you’re ready to buy a tier 3 item, so it doesn’t slow your progress towards your final build even if you sell it. Second, you can buy it at level 1, and the damage against players will stay better all the way until you finish a tier 3 item. At worst it puts you 30 seconds further from your optimal build, but in exchange it makes you cause extreme emotional trauma to anyone who meets you in the early game.
It actually annoys me a bit that the banner is just plain superior.