Can't tell for the Republic of China but I can try to tell from the PRC perspective (of course this will be biased towards the PRC's angle, just putting this out here).

Chiang Kai Shek, as the leader of the nationalists, was portrayed very poorly in the earlier days of the PRC. This has to do with so many factors:

1. Chiang Kai Shek launched the 412 incident that purged (suspected) socialist/communist elements from the cooperative government, causing the end of 第一次国共合作 (the first cooperation between the Nationalists and the Communists)
2. Chiang Kai Shek wanted to pacify the communists first before fighting the Japanese, known in China as 攘外必先安内. This was after the Japanese occupied Northeastern China (Manchuria). It led to the Xi'an incident during which two generals kidnapped Chiang Kai Shek and forced him to cooperate with the communists.
3. Chiang Kai Shek was known to corroborate with 杜月笙 Du Yuesheng, a notable gangster in Shanghai. He was also known to use assassins and secret police to get rid of his opponents.
4. Chiang Kai Shek was portrayed in PRC propaganda as a Japanese corroborator earlier on due to his 不抵抗政策, the policy of no resistance.

Let's actually go through with Chiang Kai Shek's appearances in the mainland media throughout the years:

1. Earlier on, his "title" is 人民公敌蒋介石 Chiang Kai Shek, the enemy of the people. This title was first known to come from a little book written by Mao's secretary, 陈伯达 Chen Boda. The original quote was "蒋介石是窃国大盗，是屠杀人民的刽子手，是罪大恶极的卖国贼。" (Chiang Kai Shek is a thief that stole the nation, he is a executioner that massacres the people, he is a criminal thief who sold out his nation.) This was pretty much the official notion for Chiang Kai Shek. When Chiang Kai Shek died in 1975, Xinhua News (official news for China) posted the news as "国民党反动派的头子，中国人民的公敌蒋介石，四月五日在台湾病死。(The boss of the nationalist counterrevolutionaries, the enemy of the Chinese people Chiang Kai Shek, died April 5th in Taiwan.)“ Worth noticing is that 病死 (died from disease) was used instead of 病逝 (passed away from disease). The latter is often used for respected people and the former is not.
2. His first appearance on screen is in the movie 吉鸿昌 (Ji Hongchang, the titular character was a general who was ordered to death by Chiang Kai Shek) made in 1979. Of course during his time on screen, special care was taken to make him look evil. The film used special camera angles and lighting, together with villainy scripts to make him sound extra evil. This is of course, according to everything that happened before.
3. The next notable appearance is 西安事变 (Xi'an Incident, as I mentioned above). As China just left the Mao era and entered the Deng era, the policy towards the Republic of China shifted more from hostility to attempt to unify. Thus, the portrayal of Chiang Kai Shek shifted more from a comic book villain towards a fleshed out villain. In the film he was no longer portrayed as a being of pure evil, but more of a character who has actual thoughts towards events.
4. Then comes 血战台儿庄 (The Bloody Battle of Tai'er Zhuang, a notable victory of the Nationalist Army led by General Li Zongren against the Japanese invaders). This is probably the first notable appearance of Chiang Kai Shek that was positive. In this portrayal, he was holding a remembrance ceremony for 王铭章 Wang Mingzhang, a general who died fighting the Japanese, despite the Japanese planes flying by. This is also the first movie in the mainland that portrayed the Nationalists fighting the Japanese. Before this, the Nationalists were often put in negative betrayals as either bandits who harass civilians or as lapdogs of the Japanese occupation. The background events of this portrayal is very interesting. In 1982, Liao Chengzhi 廖承志, son of Liao Zhongkai 廖仲恺 (an important character in the Nationalist Party), wrote to Jiang Jingguo 蒋经国 (son of Chiang Kai Shek and leader of RoC at the time) in a semi-official manner. During this letter, he used the phrase "度尽劫波兄弟在，相逢一笑泯恩仇。(After the turbulence as long as brothers are still alive, we can meet up, have a laugh and forget all the unpleasantness in the past.)" and also called to Jiang Jingguo to "共图振兴中华之大业 (together plan for the greatness of making China great)". While Liao Chengzhi died in 1983, this letter made great efforts in improving the relationship between RoC and PRC. Jiang Jingguo watched the movie and said "Looks like the Mainlanders admit we fought the Japanese from the looks of this movie. This movie did not sling mud at my father. Looks like they are adjusting their policy towards Taiwan. We should make adjustments as well."
5. 1989, 40th year anniversary of the PRC, the movie 开国大典 (The Founding Ceremony of the PRC) was made. Before this in 1987, Jiang Jingguo removed the martial law in Taiwan since 1949 and allowed people in Taiwan to visit the Mainland. Jiang Jingguo died in 1988, a few months after he made this decision. This time, Chiang Kai Shek was portrayed a very fleshed out (and more neutral) character. One of my tearjerkers for the movie was when Chiang Kai Shek's grandson asked him "Grandpa, where are we going?" Chiang Kai Shek answered "to somewhere far away." The grandson then asked "Will we come back?" Chiang Kai Shek replied "we will."
6. Time Jump: 2009 建国大业 (Founding of a Republic). Background: In 2005, leaders of the Nationalists, Lian Zhan and Song Chuyu visited the mainland after DPP won the elections. Both Li Denghui and Chen Shuibian, winners of the elections, were large Taiwan Independence movement supporters. This time, he was portrayed as a more positive character that opposed Taiwan's independence (which makes sense for him historically). Historically, Chiang Kai Shek opposed the claims of Two Chinas due to him wanting to reconquer the Mainland. Some notable quotes from Chiang Kai Shek in this portrayal are "反，亡党！不反，亡国！难啊！(If I am against corruption, the party will fail, if I don't the nation will fall, this is a hard choice)" and "南北朝可以出现在过去，但绝不会出现在今天！谁敢当这个千古的罪人？这胆量，我没有！(The South and North Dynasty can happen in the past, but not today! Who dares to be this sinner of a thousand years? I have not the guts to do so.)"

We can see that the portrayal of Chiang Kai Shek shifts with the political background of the movie. Thus, Chiang Kai Shek changed from an early comic book villain to a more fleshed out historical character.

I hope you guys liked the answers. If you want to see the movies, I have links in the posts for the movies. I'd love if someone can tell me the RoC side of things.