Short answer: use a direct-mutual-fund platform (no distributor commission) — top, widely‑used options in India for lump‑sum investments are Groww, Kuvera, ET Money, Paytm Money and Zerodha Coin. Which is “best” depends on whether you prioritise lowest cost, ease-of-use, research/tools or consolidated demat holdings. (amfiindia.com)

Why direct platforms matter

• Direct plans have lower expense ratios (no distributor commission) and therefore tend to produce higher long‑term returns vs regular plans. (amfiindia.com)

Quick comparison (practical differences)

• Groww — easy UI, wide fund coverage, and advertises zero charges for investing/redeeming in direct plans (convenient for lump sums). (groww.in)
• Kuvera — goal‑based planning, portfolio import, focuses only on direct plans and is free to use; good if you want planning tools plus zero commission. (kuvera.in)
• ET Money — paperless KYC, direct plans and portfolio tracking, plus additional tools (automatic switching, goal features). Good for consolidation and quick lump‑sum buying. (etmoney.com)
• Paytm Money — direct plans, low/no commissions and 100% digital onboarding (popular for simple, low‑cost investing). (paytm.com)
• Zerodha Coin — direct mutual funds (including demat option). Useful if you prefer holding MF units in demat or want everything in one broker account — watch for any demat/transaction charges if you use demat mode. (zerodha.com)

When to instead use AMC websites or registrar portals

• If absolute lowest possible cost is the primary goal, investing directly on the AMC’s website (or registrar portals like CAMS/KFin) gives you direct plans with the fewest intermediaries — but you’ll need to manage multiple AMC logins if you use many funds. (amfiindia.com)

Practical checklist for a lump‑sum MF investment

1. Pick platform (one of the above) and complete e‑KYC (PAN, Aadhaar/KYC docs or video KYC).
2. Choose “Direct” plan (not “Regular”) when placing the order. (amfiindia.com)
3. Use bank transfer/UPI/netbanking for the lump sum; confirm cutoff times for NAV on the platform.
4. Keep transaction receipts and confirm units allotted in your account/statement.
5. If you already hold regular plans, consider switching to direct plans (many platforms can do this). (etmoney.com)

One‑line recommendation by priority

• Lowest ongoing cost: AMC websites or Kuvera/Groww/ET Money (direct plans). (kuvera.in)
• Best if you want demat consolidation: Zerodha Coin (check demat/transaction terms). (zerodha.com)

If you want, tell me your priority (absolute lowest cost, simplest UX, demat consolidation, or NRI status) and I’ll recommend one platform and outline exact next steps for a lump‑sum purchase.