That would be Improved Light Tank div as the Advanced Light Tank [1943] is a bde, not a division.
The reason to NOT build Light Tank divisions is that they do NOT benefit from obsolete upgrading. Armor-II tank divisions also upgrade to basic medium armor [armor-III], and if you keep an old serial run going for the ArmorII, you can eventually benefit from obsolete upgrading by the time that you research ArmorIV [improved armor]. A long series of ArmorII can also be started much earlier for most countries, and this can benefit greatly from gearing which is always the cheapest way to build, while you usually have to research improved light tanks [1939] before you can build them.