The S21 Plus and S21 Ultra are standout models from Samsung released earlier this year. The S21 Ultra stands at the pinnacle, equipped with Samsung's best technologies, while the S21 Plus holds its ground as a mid-range device in this year's Galaxy S21 series. Both are valuable choices for consumers. However, with a budget ranging from 17-20 million VND, you have the option to buy a new S21 Plus or a used S21 Ultra.
Comparing the prices of a new S21 Plus and a used S21 Ultra
– Price of the new S21 Plus (reference at Cellphones):
S21 Plus 8GB/128GB: 16,400,000 VND
S21 Plus 8GB/256GB: 18,300,000 VND
– When it comes to the used S21 Ultra, the prices vary based on storage capacity and the condition of the device. Typically, 99% condition S21 Ultra models range from 18 to 22 million VND or more for the 512GB variant.
Comparing specifications and features between S21 Plus and used S21 Ultra
Even in its pre-owned state, the S21 Ultra retains the same features and functionalities as the new model.

In terms of exterior design, both phones share a similar design language as they belong to the same S21 series. The difference lies in the overall dimensions (S21 Ultra: 165.1 x 75.6 x 8.9 mm, S21 Plus: 161.5 x 75.6 x 8.9 mm) and the rear camera setup. The S21 Ultra boasts a larger and more powerful design with four lenses and one sensor compared to the three lenses on the S21 Plus.
Both phones feature a metal frame along with Gorilla Glass Victus on the front and back. The rear, in particular, has a matte finish for enhanced aesthetics, reducing the visibility of fingerprints.
S21 Plus and S21 Ultra, both come equipped with Samsung's Exynos 2100 or Qualcomm's Snapdragon 888 for products in the US, Korea, and Hong Kong markets. These chipsets, produced on the advanced 5nm process, feature 8 cores with clock speeds up to 2.9 GHz, delivering optimal performance and energy efficiency.
These are highly ranked chips, ensuring users a smooth experience in handling tasks without lag or stuttering in resource-intensive applications. Additionally, these chipsets support high-speed 5G connectivity.

The significant differences between these two phones lie in the display, camera setup, and battery capacity.
– Display Quality
The S21 Plus slightly steps back, whereas the S21 Ultra boasts a premium display with significant improvements. Specifically, the Galaxy S21 Plus features a flatter design, a 6.7-inch screen with a resolution of 2400×1080 (equivalent to FHD+). It also has a 120Hz refresh rate on the Dynamic AMOLED 2x display, but the compatibility range is from 48Hz to 120Hz.
As for the S21 Ultra, its screen is curved on both the left and right edges, slightly larger at 6.8 inches, with a higher WQHD+ resolution for more detailed visuals. It can simultaneously display at a 120Hz refresh rate (with compatibility ranging from 10Hz to 120Hz, aiding in power efficiency).

– Camera
You'll find a triple rear camera setup on the S21 Plus, comprising a 12MP main camera, a 12MP ultra-wide camera, and a 64MP telephoto camera. On the front, there's a 10MP selfie camera. The S21 Plus supports 3X optical zoom and 30X digital zoom.
On the other hand, the S21 Ultra boasts a more powerful camera system. It features a 108MP main camera, a 12MP ultra-wide camera, and two 10MP telephoto cameras. One telephoto camera supports 3X optical zoom, while the other supports 10X optical zoom, with a Space Zoom capability of up to 100X. Additionally, there's a laser autofocus sensor to aid in tracking subjects in your photos. The front-facing selfie camera on the S21 Ultra has also been upgraded to a 40MP sensor.

However, both phones share the same camera software, offering features like single-tap capture, 8K video recording, Director’s view for video, and photography elements such as portrait mode, image stabilization, and night mode. The S21 Ultra benefits from an enhanced Bright Night sensor, resulting in improved low-light photography compared to the S21 Plus.
– Battery Capacity
The S21 Plus comes with a 4800mAh battery, while the S21 Ultra is equipped with a larger 5000mAh battery.
A special feature exclusive to the S21 Ultra, not found in the S21 Plus, is the compatibility with the S Pen stylus.
Your Choice: New S21 Plus or Used S21 Ultra
If you desire the most powerful and modern phone with a top-notch display, exceptional photography capabilities, and extensive zoom, all within a reasonable budget, then a used S21 Ultra is the ideal choice. Ensure to hone your inspection skills before purchasing and explore reputable sellers with excellent warranty options to secure the best-quality used S21 Ultra.
On the other hand, if you need a phone with sufficient power and good camera performance without the hassle of intensive inspection and purchase considerations, the S21 Plus is a suitable option.