I'm going to elaborate on matchups because theres still lots of n4ps out there:
fw has limitless potential. Compared to other builds that are restricted by the skill they use (ie. short range vs long range matchups) and really don't have a chance to win a certain matchupl, fw is lethal against everything. It's also one of the simplest builds to master...most builds have multiple attacks, and they need to look for openings to make those attacks, knowing when they can or can't get the kill. Fw is just tele tele tele fw, tele tele tele fw constantly pressuring everything.
This simplicity makes for some pretty easy duels, as always, I consider matchups as if I were dueling myself:
Hammerdin
If you can beat a decent-good hammerdin on a fw sorc, you can beat the best hammerdin just as easily...spam frost nova, don't tele in hammers, fw. If you have good mana and screw up and tele into hammers once or twice you'll probably still win.
Trapper
This one takes a bit more strategy if you want to call it that...but it carries a similar idea, any decent-good trapper will sit in traps, try to avoid fw, and mb you. The best trapper ever will duel the exact same way. Use the corners and c/t and drop walls on the trapper where you can't get mb'd, if you see an opening where they don't have traps, go for it and let them namelock you when you drop the fw. Just like hammerdin, if you can master this strategy you can beat any trapper. You can still screw up a few times and win thanks to our friend WSG.
Plague
Charge in w/ 0 life and lose vs stay back and rep and win. Pretty obvious...just threw it in because people still bring it up lol
The next 3 classes are the sorcs "weaknesses".
Charger
The weakness in this case is randomness. If the duel isn't completely boring and l8zy, you're going to be tanking some 2h charges. Stand next to a puddle/wall/river etc. so that if the charge does hit, it won't be a kb + multiple hit. Use invisible fws a lot, overall pretty boring duels >_<
Fb Sorc
The threat here is a good unexpected jump or just constant pressure. IMO equally geared, the fb has a slight advantage. If the fber is constantly locking you, walk along a fw and tele away when they jump you. Every fber ever will cast fb after they jump a lock, so they'll take a good amount of damage. Overall pretty fun/dynamic duels.
Tele Druid
Same as fb sorc, but less of a threat from a single unexpected jump, because even after 1-2 nados you should still be able to just tele away. A tele druid has a chance to take down a fwer with good constant pressure, but doesn't have as many opportunities to do it with a tele staff. Fw has a decent advantage, still fun duels though.
Tele Barb
Worth mentioning because its probably the single greatest LLD invention of all time. Basically a combination of charger/tele druid when it comes to dueling fw sorcs. Relies on good pressure + good hit checks and crits etc. Fw still has a good advantage.
lmk if I missed anything