Short answer — choose by how you charge:

• If you want fastest wired charging and highest capacity: get a USB‑C Power Delivery (PD) bank with at least 20 W output (better: 30 W+) so your iPhone can fast‑charge. Apple says iPhones fast‑charge with a 20 W (or higher) USB‑C PD adapter. (support.apple.com)

• If you want magnetic convenience (stick it to the back): buy a MagSafe / Qi‑2 magnetic power bank. These are easier to use on the go but are usually slower than wired PD (many support 7.5–15 W wireless). Check compatibility with your iPhone model and case. (anker.com)

Recommended picks (good for iPhones — mix of wired, magnetic, and pocket options)

• Anker 737 (PowerCore 24K) — high capacity (24,000 mAh), USB‑C PD, up to very high outputs for multiple devices; great if you want many full phone charges or to charge a laptop + phone. Good choice for travel/power users. (anker.com)

• Anker MagGo power banks (MagGo 10K / 5K) — slim, strong magnets, Qi2/MagSafe‑style magnetic wireless charging (up to ~15 W on some models) and often include a USB‑C port for wired charging. Nice balance of convenience + decent capacity. (anker.com)

• Belkin BoostCharge Magnetic Portable Wireless Charger (10,000 mAh) — reliable MagSafe‑compatible option, can be used as a wireless pad and a portable bank; good fit if you want MagSafe alignment plus pass‑through charging. (Note: check model and recalls historically; see safety note below.) (belkin.com)

• Mophie Powerstation Plus (10,000 mAh, integrated cables) — excellent if you don’t want to carry cables: available with integrated Lightning / USB‑C cables and 20–30 W outputs so you can fast charge iPhones directly. (mophie.com)

• OtterBox MagSafe power banks (3K / 5K) — small magnetic banks that are rugged and pocketable; good for short top‑ups and MagSafe users who want a durable unit. (otterbox.com)

Tips when you buy

• Match output to need: for fast wired charging pick a PD bank rated ≥20 W (30 W gives more headroom); for MagSafe convenience expect slower wireless charging (commonly 7.5–15 W). (support.apple.com)
• Check ports & cable needs: iPhone 15+ uses USB‑C natively — wired PD banks with USB‑C to USB‑C are ideal; older Lightning iPhones need a USB‑C to Lightning cable (MFi certified). (support.apple.com)
• Capacity vs size: 10,000 mAh = ~1–2 full iPhone charges; 20,000–24,000 mAh = multiple full charges but bigger/heavier. Manufacturer estimates vary. (anker.com)
• Safety & recalls: buy from reputable brands and check for recalls. (There have been recalls/notices in recent years for some MagSafe banks from major brands — verify the exact model before use.) (theverge.com)

If you tell me which iPhone model you have (or whether you prefer magnetic vs. wired, light pocket carry vs. travel pack, and your budget), I can narrow this to the 2–3 best current models and give links to purchase.