When choosing a penis pump, there are a few factors to consider, including:

1. Size: It's important to choose a pump that fits your penis comfortably. Most pumps come with a standard size cylinder, but some models offer different sizes or adjustable cylinders.
2. Material: Penis pumps can be made of various materials, such as plastic, acrylic, or silicone. Consider the material's durability, ease of cleaning, and comfort when choosing a pump.
3. Pump type: There are two types of penis pumps: manual and electric. Manual pumps require you to pump the device by hand, while electric pumps use a motor to create the vacuum. Electric pumps may be more convenient for some users, but they are typically more expensive than manual pumps.
4. Pressure gauge: Some penis pumps come with a pressure gauge that allows you to monitor the amount of pressure inside the cylinder. This can help you avoid over-pumping, which can cause injury or discomfort.
5. Price: Penis pumps can range in price from less than $20 to several hundred dollars. Consider your budget and the features that are most important to you when choosing a pump.

It's also important to choose a reputable manufacturer and to read reviews and product descriptions before making a purchase. Additionally, if you have a medical condition or are taking medication, it's a good idea to consult a healthcare professional before using a penis pump.