The OnePlus 9 Pro and Samsung Galaxy S21 Ultra are two of the most powerful Android smartphones released in 2021, each offering flagship-level performance, premium design, and advanced camera systems. While the OnePlus 9 Pro focuses on delivering high-end specs at a relatively lower price, the S21 Ultra represents Samsung’s top-tier innovation with superior zoom capabilities, a brighter display, and S Pen support. Both devices remain relevant in 2025, especially in the refurbished market, where they offer excellent value for money.
Key Highlights
| Feature | OnePlus 9 Pro | Samsung Galaxy S21 Ultra |
|---|---|---|
| Organization Name | OnePlus | Samsung |
| Launch Date | March 2021 | January 2021 |
| Starting Price (2025 Refurbished) | ~$200 | ~$200 |
| Display | 6.7″ LTPO AMOLED, 120Hz | 6.8″ Dynamic AMOLED 2X, 120Hz |
| Official Website | oneplus.com | samsung.com |
Design and Build Quality
The OnePlus 9 Pro features a sleek, glossy finish with a curved AMOLED display and an aluminum frame, weighing 197g. It comes in Morning Mist, Pine Green, and Stellar Black, though the glossy back attracts fingerprints easily. The Samsung Galaxy S21 Ultra, on the other hand, has a more industrial design with a contoured camera module that blends into the frame. It weighs 227–229g, making it noticeably heavier, but it also offers Gorilla Glass Victus (vs. Gorilla Glass 5 on the OnePlus) for better drop protection.
Both phones are IP68-rated for dust and water resistance, but the S21 Ultra stands out with S Pen support, a feature previously exclusive to Samsung’s Note series. The OnePlus 9 Pro has a more compact form factor, making it slightly easier to handle, but the S21 Ultra’s premium build and added functionality give it an edge in durability and usability.
Display Comparison
The OnePlus 9 Pro boasts a 6.7-inch LTPO Fluid AMOLED display with a 1Hz–120Hz adaptive refresh rate, ensuring smooth scrolling while conserving battery. It supports HDR10+ and reaches 1300 nits peak brightness, making it great for media consumption. However, the Samsung Galaxy S21 Ultra’s 6.8-inch Dynamic AMOLED 2X panel is even brighter at 1500 nits, with superior color accuracy and a 10Hz–120Hz adaptive refresh rate.
While both screens are QHD+ (1440p), Samsung’s higher brightness and better outdoor visibility make it the winner for users who prioritize display quality. Additionally, the S21 Ultra’s lower minimum refresh rate (10Hz vs. 1Hz) doesn’t impact battery life as much as expected, thanks to Samsung’s efficient optimization.
Performance and Software
Both phones are powered by the Qualcomm Snapdragon 888 (in most regions), paired with up to 16GB RAM on the S21 Ultra and 12GB on the OnePlus 9 Pro. In benchmarks, the OnePlus 9 Pro scores slightly higher in AnTuTu (975K vs. 843K), but real-world performance is nearly identical.
Where they differ is software support. Samsung promises four major Android updates, meaning the S21 Ultra will get Android 15, while OnePlus guarantees up to Android 14. Samsung’s One UI is also more feature-rich, with DeX mode, better multitasking, and S Pen integration, whereas OxygenOS offers a cleaner, near-stock Android experience.
Gaming performance is excellent on both, but the Snapdragon 888 tends to throttle under heavy loads, causing heating issues in prolonged sessions. The S21 Ultra’s vapor chamber cooling helps slightly, but neither device is ideal for hardcore gamers.
Camera Showdown
The OnePlus 9 Pro features a 48MP main sensor (Sony IMX789), 50MP ultrawide (IMX766), and an 8MP telephoto (3.3x zoom). Thanks to Hasselblad tuning, colors are more natural compared to Samsung’s saturated output. However, the S21 Ultra’s 108MP main sensor, dual telephoto lenses (3x and 10x optical zoom), and laser autofocus make it the superior camera phone.
In low light, the S21 Ultra captures more detail with less noise, while the OnePlus 9 Pro struggles with grain. The ultrawide cameras are comparable, but Samsung’s 12MP sensor has better distortion control. For zoom photography, the S21 Ultra’s 10x periscope lens is unmatched, allowing for 100x Space Zoom (though with diminishing quality).
Selfies are better on the S21 Ultra (40MP vs. 16MP), and its 8K video recording is more stable. The OnePlus 9 Pro does support 8K@30fps and 4K@120fps, but Samsung’s Super Steady stabilization gives it the edge for videography.
Battery Life and Charging
The S21 Ultra’s 5,000mAh battery outlasts the OnePlus 9 Pro’s 4,500mAh cell, especially in adaptive refresh rate mode. However, OnePlus dominates charging speeds with 65W wired and 50W wireless charging, refueling the battery in just 32 minutes. Samsung maxes out at 25W wired and 15W wireless, taking over 70 minutes for a full charge.
Both support reverse wireless charging, but the OnePlus 9 Pro’s faster top-up makes it more convenient for users who need quick power boosts.
Price and Value in 2025
In 2025, refurbished models of both phones are available for around $200, making them excellent budget flagship options. The S21 Ultra is better for photography, display quality, and long-term software support, while the OnePlus 9 Pro wins in charging speed, lighter design, and cleaner software.
FAQs
1. Which phone has better battery life, the OnePlus 9 Pro or S21 Ultra?
The S21 Ultra lasts longer due to its 5,000mAh battery, but the OnePlus 9 Pro charges significantly faster (65W vs. 25W).
2. Does the OnePlus 9 Pro have better cameras than the S21 Ultra?
No, the S21 Ultra’s 108MP sensor, dual telephoto lenses, and superior low-light performance make it the better camera phone.
3. Which phone will get more Android updates?
The S21 Ultra will receive updates up to Android 15, while the OnePlus 9 Pro stops at Android 14.
