This is the main performance indicator of the graphics card because it indicates the model of this card. The performance of cards of the same model is very similar and usually very different from the cards of another model.
The main difference is the manufacturer. NVidia produces GeForce series cards and AMD produces Radeon series cards. There are considerable differences between both series, GeForce cards have more successful (more stable) drivers, which improve the compatibility of these cards with games and operating systems reducing the image defect (artefact) and the cases of "hanging" to the minimum. Radeon cards usually are cheaper and consume less energy (they are technologically superior), however there might be problems with drivers and the support of games.
The choice between Radeon or GeForce series is the question of preference, similar to the choice between AMD or Intel CPU, and not always there is 100% rational justification behind it, therefore we recommend to base your selection criteria just on the games that you want to play in the near future and to find a video review in YouTube (the graphic card model + the game title) that will demonstrate exactly how the particular card handles the relevant game. The result will be obvious and usually quite close to what you get when you buy the particular or similar model card.
For making the choice easier for our customers TopPC.fi has marked the graphic cards (models) that are the best choice for playing all the newest games at a reasonable quality level with a green tick "recommended".