FFX-HD - Any quick/efficient ways of levelling?

When you Have access to the airship and can go anywhere? Aiming to kill One-Eyes for the triple AP weapons then do the tonberry/cactuar trick.

Where is the best place for quick/good exp?

Omega Ruins or Inside Sin.

Though I would recommend buying capture weapons and filling out your monster arena catalog first, unless you already have. Capturing 10 of everything in all zones will unlock all monster arena bosses and net you a huge amount of items for customizations and mixing. If 10 is too much, aim for 5 to get the 99 Dark Matter for your first Ribbon. By the time you get that done, One-Eye should be a breeze.

Here are some tips:

An easy way to start getting One-Eye kills if you can't take him down with character damage, is to use Anima (Bahamut if you don't have Anima yet). To improve your chances of summoning before One-Eye uses Shockwave, have Yuna out of your party and switch her in from one of your faster characters. Alternatively, Auron's Celestial Weapon has first strike and will guarantee you first turn even when ambushed. If your Aeons are not strong enough, just grind Yuna for more stats and come back. After some development, you'll be able to kill One-Eye with 2 regular attacks. He's very good for getting Dark Matter.

Kottos, in the Area Conquest list, is great for getting regular spheres. Once you start tackling Don Tonberry you'll burn through a lot of spheres. Extract Power/Mana/Speed/Ability on Kottos will net you 20 spheres each kill, or 40 for an overkill. Cast Hastega on your party, have one character with Protect and using Sentinel, while the others attack Kottos and heal your tank as needed. Eventually, you'll be able to kill Kottos quickly without the need for this strategy, but it does make it much easier early on.

Kottos can also be farmed for gil. Buy Tetra Shield from the merchant in Kilika (Should have 4 slots with +5% HP on it). They're cheap; just over 2200gil each. Kottos' common item drop, Healing Spring, can be used to customize SOS Regen to armor at a cost of 12 per job. Kottos drops 40 each overkill. Customizing SOS Regen to each Tetra Shield will change them to Regen Shield, which sells for over 37,000 gil each. There may be other ways of making gil, but that method has served me very well over the years. Quick and easy.

Nice guide, thank you... I seem to be struggeling with Omega Ruins... tbh I didn't do much grinding at all on the way here, e.g no "aga" spells yet... no holy, I've done quite abit of the hunting log. highest hp is auron at 4.2k.

Then again I should build stoneproof armor.... given that is what is stopping me in omega ruins. I havn't been back to beville even yet, let alone inside sin... maybe I should?

@MBirdy88: Aye, inside Sin will do nicely if Omega Ruins is tough. Status effects aren't much of a problem in Sin. Except perhaps for Confusion from the floating one-eyed monsters there, but you can steal Musk for Confuse-Proof.

Armor Break will go a long with Gemini, and the giant armored turtles. If you're having trouble getting Armor Break to work (some Monster Arena bosses are highly resistant to breaks), Auron's Banishing Blade overdrive will always inflict it (unless Immune). Comes in handy when you start farming Juggernaut for Strength Spheres. You'll need to collect Auron/Braska/Jecht spheres to unlock Auron's Overdrives.

If Inside Sin is a bit slow for you, then return to the dome in Zanarkand Ruins where you can kill things much more quickly (use the transport pad just below the save sphere when you arrive from the airship). It should be much breezier for you. The Defender Z enemy gives nice AP as well as Lvl 2 Key Spheres (Lvl 3 on rare drop). The Zombies can be Phoenix Down'd, but you can also Steal Candle of Life and Purifying Salt from them (The latter is used for No Encounters on armor - though capturing 5 of each Dragon/Drake type enemy will get you 99 of them)

You can always just use aeons inside omega if the monsters are too tough for your party.If Yuna has decent stats Anima and the Magus Sisters will destroy everything in there.(easily dealing 99999 per hit)

That's what i did until i got to the point where Auron can deal 50000 points of damage.