I cleared Very Hard mode with no deaths, virginity intact. If you want to save time struggling, read this weapon guide:
Reset stats using Vendetta, the woman in the starting area, often. Make a brand new stat distribution for each weapon you're using.
tl;dr Bone-carved Kris best for initial encounters, Crusader's Straight Sword (Normal) best when you've memorized enemy attack sequences. Kris early-mid game, Crusader's Sword late game. Thoughts on Magic at the bottom.
Bone-carved Kris is the best early -> mid game weapon. It is the best weapon when fighting an enemy for the first time. If you don't know this thing's move set well enough to dodge it, thrusting with the Kris and immediately retreating gives almost no opening to the enemy mob to exploit. Once you're sure you can dodge well, you can step in close with Kris's full combo.
Build: get 7 STR, then enough stamina for a sprint into range, full combo, and then sprint out of range, then 300 HP. Then 200 stamina, 400 HP, and the rest into more STR. This is because the Kris has a 1.2x STR multiplier from the start.
Crusader's Straight Sword (Normal) is the next and last weapon you need. Once you memorized an enemy's move set or has enough HP to afford making mistakes, you can step in close to an enemy to unleash full combos without being hit. Once you get here, Crusader's Straight Sword has a 4x combo, while Kris has a 3x combo, so you can have approximately 25% more dps when unleashing full combos. You can still long range thrust, actually, but the Th move (thrust) is the 2nd in the Straight Sword combo, so you could intentionally miss the first swing then use the 2nd move to stab over long range. Again, it's easier to avoid being hit if you thrust, sprint out of range, thrust again.
An advantage of Crusader's Sword is that you have to switch to an INT build, which seems to help with magic. However, magic is still too weak, so don't get more MP just to get this extra side ability.
Build: weapon requirement first, then same as above except go into INT. Don't go ascension reinforcement path to get the Corrupted Crusader's Straight Sword, because that just gives 1.1x STR and 1.1x INT multipliers so while you could keep an STR build (no reason to do so btw; STR DEX INT are only for weapon damage purposes), you're just weaker than a full INT build with the 1.2x INT multiplier on the normal holy version. Plus, the attributes of holy and dark are just very low. Still, holy is useful in the area you get the Straight Sword and the arguably hardest boss in 0.54 takes extra damage from holy.
Defender's Broadsword is a mandatory side arm. When you meet attacks that you can't dodge (I won't spoil, but I'm thinking of a very colorful attack), switch to the Defender's Broadsword and hold guard. Use spare resources to upgrade this sword at least once to go from "Guard break rate" (damage reduction % in guard position) at 80% to 90%. You don't need to meet STR requirements to use this sword to guard.
Unmarked Katana is a fancy choice you can try out. You get it midgame, way after Kris and a bit before Crusader's Sword. It does not have a thrust, its first move or two has a miniscule but significantly longer animation time compared to the above 2 weapons. It does give style points. Unmarked Katana III (Normal) upgrades the weapon from having a 3x combo to a 4x combo, making it a great rival against Crusader's Straight Sword. The only problem is that you can upgrade to III (Normal) when the game is basically over. So there is no real necessary role for the katana.
However, the Katana has 2 advantages:
1) if you step in close enough, you can hit an enemy an extra 1-2 times. A 3x combo becomes a 5x combo. A 4x combo becomes a 6x or 7x combo. This is most obvious against the testing dummy. However, you can make it work in actual combat if you are at point blank range - basically, you dodged the enemy's attack and is exploiting them while they have their animation end lag.
2) Unmarked Katana III (Normal) has the highest multiplier I've seen so far: 1.5x on Dex. I haven't actually seen this translate to extra high damage hits for some reason, though, and I'll keep testing. I haven't comprehensively looked at the upgraded versions of every weapon either.
Greatswords are really fun at first until you meet a real boss and get thrashed. The greatsword strategy is basically: you can't dodge even if you can react fast enough, so just get hit and hope you don't die, then get back your HP with revenge healing.
By the way, you actually don't do that much more damage. The Zweihander hits the test dummy way more times than would actually happen against an enemy mob, like 1 swing hits for 3 hits for some hitbox reason.
2 other strategies with greatswords:
1) Jump, midair swing, sprint out of range. You'll delete the animation ending lag this way. And you might be way out of enemy melee range if you hit from a midair position 2 meters above them. You could sometimes pull off a double midair hit using double jump. I used this a lot starting out.
2) Guard, let the enemy attack, parry perfectly, then attack. This needs a lot of practice for each enemy, so this is not a strategy versus unfamiliar enemies.
Magic is useless, but if you wanted to, Fireball is the best spell. It is very fast to cast, which means you'll be in a position to dodge. You can cast in quick succession nonstop, so this is way better than Lightning Storm. You can decimate some enemies with this. However, you don't get eternal refills of MP, while you get eternal refills of Stamina. I tried to beat all the bosses with just Fireball. It didn't work on the harder bosses because I ran out of MP. Lightning Strike is also good but harder to aim. Using
Wall of Light is very, very interesting. It is quick casting and could stop all enemy charges or escapes, unless they teleport. This solves a huge weakness of magic: needing cast time (block the enemy) or missing often with magic (box them in with a wall or two). However, it's just not feasible in the end because it costs too much MP and lasts too short.
Exploding Cross and Witch's Prayer complement each other. Exploding Cross costs MP and, if you hit, drops a healing orb. Witch's Prayer costs HP and gives MP. They make a complete loop that gives you infinite MP and HP. The only problem is you will miss with the Cross. You can trap enemies with Wall of Light but then by the time you finishing casting Cross and Prayer, the Wall expires, so the loop is unrealistic. Maybe you can make it work.
I did a lot of testing with the weapons, but am too lazy to type up a serious full guide right now, so I decided to lazily dump out the thoughts as they came to me, so I apologize if this is unorganized or overly long.