to start off with there are several grades of gundams depending on the grade is how well it will work and how easy. there is also scales on how big you want it to be the lower you go the bigger it is. and to end it all is the gundam/series you want since there is a lot.
High Grade (HG) is a line of Gunpla kits by Bandai. These kits feature better range of motion and greater poseability than most No-Grade kits.
Perfect Grade
Perfect Grade (PG) is a series of 1/60 scale Gunpla kits created by Bandai. The PG line originated with the release of the Perfect Grade Evangelion EVA-01 in 1997. The line was later transferred to the Gundam franchise in 1998 and aexclusive to Gundam until 2017, when Bandai announced the Perfect Grade 1/72 scale Millennium Falcon for the Star Wars franchise. The PG line has significant external and internal details plus light up gimmicks with LEDs. The PGs are some of the most expensive Gunpla produced and have often been used to develop Master Grade and Real Grade technology.
Master Grade (MG) is a line of 1/100 scale Gunpla kits of the Mobile Suits in the Gundam meta series. The series was first produced in 1995 as part of the Gundam 15th Anniversary project.Master Grade kits differ from other 1/100 scale Gunpla, with their level of detail, articulation, and proportions being second only to the Perfect Grade line. A majority of MG kits feature a skeletal inner frame with working hydraulics, some also accommodate Gunpla LED Units for light-up gimmicks. To give viewers a perspective of the Mobile Suit's size, many MG kits come with 1/100 scale figurines of the pilots or key characters of their respective series. In addition, some kits include 1/20 scale character figures.
Real Grade
Real Grade (RG) is a line of Gunpla kits by Bandai that was introduced in 2010 as part of the Gundam 30th Anniversary commemoration project. These consist of Mobile Suits from both the Universal Century and the Alternate Centuries. The RG line combines the best aspects of the other three Gunpla lines: The small size and affordable prices of the High Grade, the advanced inner frame technology of the Master Grade and the massive parts count and details of the Perfect Grade. The tagline for the RG line is "Excitement Embodied". Also, the RG line reflects what a mobile suit would look like if it were built in the present day.
Mega Size Model (MSM) is a line of 1/48 scale Gunpla kits of Mobile Suits from the Mobile Suit Gundam and Mobile Suit Gundam AGE TV series. Despite being the largest scale Gunpla line, Mega Size Model is priced lower than the 1/60 scale Perfect Grade due to a smaller parts count. Detail and articulation are equal to High Grade kits. As this line is geared toward beginners, the runner gates are thin enough to separate from the parts without the need of a nipper; each kit comes with a Double Separator to easily remove parts from the runner or separate two halves of a part. Some runners are designed to be broken in half and "sandwiched" for quick assembly. Each kit includes a water slide decal sheet. The first four kits included a how-to guide by Hobby Japan and Dengeki Hobby; the rest of the series has a beginner's guide included on the instruction manual.