High Grade kits are the most collectible because the selection of Gundams and mobile suits in this class, whether it's a main character or another type of mobile suit, is enormous, and High Grade is one of the most affordable types apart from Super Deformed kits.

High Grade kits are made in scales: 1/144, which is about 13 cm high, depending on the model. Some models are slightly taller like Sinanju and Sazabi, while some HG models are somewhat shorter like Exia. 1/144 kits are nice to assemble and display in showcases because they take up less space than Master Grade or Perfect Grade kits.

You can easily tell if it's a High Grade kit because it will have the abbreviations "HG" on the box, and the box format is horizontal.
The ability to pose the models has improved over the years. In older High Grade models in the 90s, the articulation of HG kits was limited but satisfactory, but in recent years, Gunpla technology has made great strides, and the articulation of newer HG kits is excellent, making them comparable to Master Class kits!

High Grade kits are suitable for anyone starting their Gundam journey.

Example of a common 1/144 HG box: