To me, the most dramatic difference is that Gould and Sutherland brought a real edginess to their characters which is wholly missing in the portrayal of their characters by their TV counterparts. In 1970, Gould and Sutherland were part of Hollywood's hip counter culture elite which gave them street cred and they seemed much cooler than the "whitebread" TV actors. The TV show definitely had more talented comedy writers.
Hey, I absolutely prefer the movie over the TV series, ultimately, but don't diss Alan Alda. He's an incredibly talented actor and IMO has always maintained a level of cool. McLean Stevenson and Larry Linville were also great in the series. The problem with the TV show is that it's a TV show, and there is less freedom of expression to be had when you have television censors to get past. Altman had the freedom to be his audacious self in making the film because he didn't have to worry about Standards and Practices.
Television and film are much different formats than many people think, and I think this was especially true in the past. You can't expect a TV series to show the same level of daring as a theatrical movie based on the same material. It's just not a fair comparison.
I'd choose film over series if I had to, but the series had its merits as well.
Let us take the risks of peace upon our lives, not impose the risks of war upon the world.
That's part of why I think TV and film were so different in the past - we didn't have HBO and Showtime, and even after we did, it was a long time before they started showing series. When I was a kid in the 80's, HBO showed nothing but movies. But today they can put series and miniseries on premium cable networks, so they can get away with much more risque stuff than on network.
Let us take the risks of peace upon our lives, not impose the risks of war upon the world.
Alan Alda is very talented and I have enjoyed him in everything I have seen him in (brilliant work in The Avaitor and two Woody films, Crimes And Misdemeanors and Manhattan Murder Mystery). But the changes they made in the Hawkeye and Trapper characters and their relationship in the TV show causes me to think Alda has a huge ego. Trapper in the film was the brilliant surgeon who was named chief surgeon (the celebration party in Trapper's honor led to the great microphone scene). Nothing was said about Hawkeye's surgical ability. The issue of the doctors' competence was not part of the film like it was in often in the series. But I wondered why CBS decided to make Hawkeye the star and make Trapper a supporting character, Hawkeye's fun loving sidekick. Did Alda insist on it before he would take the part? He was a more famous and accomplished actor than Rogers when the show was cast (and more talented, frankly). And Alda's father Robert was a well-known actor. Perhaps CBS believed Alda was important enough to agree to make Hawkeye the definite star of the series instead of a true ensemble piece. There was no reason to not make the hard partying Trapper the brilliant surgeon and star and make Hawkeye his more low key, sensitive and loveable sidekick who sometimes needed to get Trapper out of jams and offer advice. They would have had to hire a stronger actor than Rogers to be the center of the series, but it could have gone that way.
I have to say I prefer the film. Not only was it directed by one of the great directors (even if this was early in his career) and starred some great actors, it had darker themes and a grittiness that wasn't (and at the time couldn't be) in the TV show. I liked the later series (with Winchester and B.J. et al) as I think it was closer to the film (certain characters, or at least character names aside) and had the "horror of war" rather than just the "let's have a laugh" attitude of much of the earlier seasons.
Neither era tops the film for me but at least the later season of the TV show came closer (in a TV format) than the earlier years.