Short answer: there isn’t one absolute winner — it depends on what you want (designer vs fast‑fashion vs second‑hand). Below are the top Australian online destinations that regularly give the biggest discounts, grouped by what they’re best for and why.

• Best for broad selection + reliable Aussie sales and free returns: THE ICONIC — large local inventory, frequent seasonal/clearance sales and sitewide deals, free/fast delivery thresholds and easy returns. (theiconic.com.au)

• Best for deep designer discounts (luxury at big markdowns): THE OUTNET (and similar outlet/“off‑price” sites) — constant outlet-style markdowns and flash sales with discounts often 50–70% or more. Good if you hunt for past‑season designer pieces. (elle.com.au)

• Best for the biggest percentage off fast‑fashion and frequent promo codes: boohoo and ASOS — frequent sitewide sales, app‑only deals and student discounts that stack with big clearance drops (some campaigns/clears reach very high % off). (buckscoop.com.au)

• Best for flash/private sales and very large clearance events: Ozsale / Brand-sale clubs — member-only events and flash sales that regularly advertise 40–80% off designer and high‑street brands. Good for bargain hunting if you check often. (marieclaire.com.au)

• Best for the lowest prices if you’re happy with pre‑owned or marketplace finds: Vinted / Depop / eBay Australia — huge selection of secondhand and new‑stock bargains; often the cheapest route for labeled items or unique low‑cost pieces. (au.marketscreener.com)

Extra context and money‑saving tips

• Timing matters: major events (end‑of‑season, Black Friday/Cyber Monday, Boxing Day) are when most retailers give their deepest discounts — plan around those if you can. (techradar.com)
• Stackable savings: sign up for newsletters or apps (welcome codes), use student verification (ASOS/Boohoo/Outnet offer student discounts), watch app‑only previews, and combine with cashback sites where possible. (asos.com)
• If you want designer labels specifically, prioritize outlet/flash‑sale sites (Outnet, Ozsale, BrandAlley). If you want everyday cheap new clothes, fast‑fashion retailers (boohoo, ASOS) usually give the steepest percent markdowns. (elle.com.au)

If you tell me whether you want designer labels, fast‑fashion, or second‑hand bargains (and whether size/brand matters), I can pick the single best store for your needs and show current deals.