Probably generally the later ones although Seasons 1-3 were very good. I feel however some of the early characters did not transition well as the show changed, especially Frank Burns and Radar. Seasons 4-5 were the worst of the bunch and I think when Winchester joined it really got a lease of new life.

Early seasons.

all my favourite episodes are in the first three seasons. Wouldn't have minded Henry being replaced with Potter so much if they hadn't killed henry off. But Trapper being replaced with b.J. ws a disaster for me.

But, Larry Linville's last season was better because the two character evolved as Houlihan was in love with Penobscot and Burns was hurting.
I wish they had developed Frank off of the last scene in "Margaret's Engagement" when he's talking with Hawkeye about picking up some girls, in particular a young nurse then gets off a good smack on Hoolihan.
Instead they had him devolve into an even more spiteful and hateful character that was (IMO) totally insufferable, and Margaret was little better. I was glad to see him leave after S-5.

I don't go so much for seasons as I do for phases/evolution.
Burns/Houlihan was good at first, but probabhly lasted one season too many.
But, Larry Linville's last season was better because the two character evolved as Houlihan was in love with Penobscot and Burns was hurting.
Trapper and Blake were great, and they probably could have lasted longer before people got tired of them.
Houlihan eolved again when marriage broke up and became more serious.
I found Kingler to be the most interesting character. I liked him in his early "dress" years as well as later when he became company clerk. The characted evolved over the 10 years at a good pace, just as you got tired of the old one.
Hawkeye is the one who evolved the least.

Does it count if he cheated on his TV wife with his wife in real life?

True, he did, but he agonized about it and beat himself up over it and then gave the girl the brush off, and after that he became more and more dedicated to his wife.

BJ cheated on his wife once.

Later for meI liked Charles', and how he could give it as good as he got itI also liked the fact that Col. Potter & BJ, while tempted at times, did remain faithful to their spouses unlike Henry and Trapper who were little horn dogs after everything and anythingThis reason alone is why I detested both Henry and TrapperHenry wasn't a leader, Potter while IMHO a little to lenient with especially Hawkeye, was military and did adhere to military protocol, whereas Henry was just a doof who never should've been placed in a command position.
"Life is like a banquet and most poor suckers are starving to death."

Ideally I would like to combine the best elements of both, Blake and Radar were definitely more interesting and better suited to each other than Potter and Radar. A more mature Radar was also better than the childlike one he became.
Winchester over Frank.
Hawkeye not moralizing as much as he did later on.
Sometimes a movie or tv show plot is so stupid that only the stupid can understand it.

I prefer the later ones, because that's when I first got into the show. "Life Time" was the first full episode I watched, and I became more familiar with Seasons 8-11. The earlier shows felt too much like a different show. In fact, Season 1 closely resembles Hogan's Heroes.

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I like the earlier seasons better because like the funny episodes better than the serious ones.However two of my favorite latter-season episodes that I Iike because they were pretty much all comedy are No Sweat and The Moon is Not Blue.

The early ones. I loved the chemistry between Radar and Henry.

1-4 and 6.
When I'm watching my disks those are the seasons I usually watch, though maybe once a year my wife and I will marathon the entire series.
I liked S-4 when BJ and Potter first came onboard and S-6 when Charles comes aboard.
I probably like S-5 least; Frank is on his own. Margaret is insufferable with her "Donald Penobscot" bs and Frank is so spiteful and humorless that I was really happy to see him go.
It's more of a personal thing, but when S-7 started I had graduated nursing school and was working 3-11pm so I saw very little of the last 5 seasons until years later; they just never grew on me like the earlier years.
Inaugeral Countdown:
15
days
16
hours
55
minutes

Season 1-3

I love the later ones. The ones without Radar. I think I have seen every episode. LOVE Winchester. My favorite episode is "Who Knew?"

Can't really answer this one until I've seen more of the first three seasons. I've only just recently got into MAS*H. Over here in the UK they're showing at least two episodes nightly on True Entertainment (Freeview Ch.61) and I was too young to catch the series first time around.
They're heavily playing the later stuff plus, for some reason, frequent weekend four-ep chunks of seasons 4/5 on rotation; but neglecting the Trapper/Henry years, with only one repeat showing of this era so far as I'm aware.
I was going to start a new thread of "what's the best mix of characters?" So far it's S.4/5: Frank to represent the early years, plus we've already got Potter & BJ on board, and Radar hasn't faded from the scene yet.

Henry Blake was a clueless buffoon, while Sherman Potter was more than competent.
Frank Burns became a pathetic punching bag, while Winchester could dish it out as well as he could take it.
Later Margaret became a woman who deserved respect, early Margaret was insufferable.
Getting Klinger back into his fatigues and out of the dresses ended a schtick that was funny at first but eventually wore out its welcome.
Definitely later seasons.

While I love Winchester, I personally prefer the first 5 seasons or so.
The writing was far better as was the comedy.
Same with
Law & Order,
I prefer the first 8 seasons of that great drama, the seasons which had better writing.

The first three seasons are all I would watch.
Same here, but the last few times I've caught an episode, I've noticed that even the first three seasons aren't as good as I remember. I'd like to watch a few episodes from just the very first season some time to see if maybe it is as good as I remember. Maybe I'd still like the first season, and maybe it just went down hill sooner than I remember.

I couldn't agree more. Once the show turned into Alda's soapbox, it really went downhill.

The first three seasons are all I would watch.
My favorite as well. You can't beat Henry.

The first three seasons are all I would watch.