O-300s - Love em? Hate em? Typical maintenance costs and overhaul cost

I imagine someone, somewhere, has an uncle who worked for Lycoming who said the same thing.
I owned a ‘64 Skyhawk C172E with an O300D. Secondly a C150 the O200A.
Presently a 68 Cherokee 140 with a O320 E2A.

first; The O200 and O300 were no smoother than the Lycoming. Sorry, could just never get mine that smooth. Even though I had it overhauled twice, second time with weight matched pistons. Two overhauls on the O200 were essentially the same. Never got more than 1,100hrs without pulling a cylinder for valve rework. Leaning was essential with 100Ll. MMO seemed to help but in retrospect was likely just a bandaid approach. My only experience was with old Continental or new Millennium cylinders.
At the first overhaul, the otherwise serviceable crank shaft was rendered unserviceable by an undetectable (circa 1963) flaw in the forging. 1994 x-ray dectected it. A serviceable crank cost me $895 in 1994. Added 20% cost to my local shop o/h! No new cranks were available even back then.

Ive got several thousand hours in several other O300’s. None are noticeably smoother than the Lycoming 4cyls. As a CFI I’ve flown dozens. My experience is that the Lycomings are hands down better for reliability. My experience with O470’s, and 520’s further my feelings. The Continentals due to induction system design with carburetors is conducive to carb icing. Experienced it many times. Never with a Lycoming. My C150 on a cool cloudy humid day could ice up taxiing from the tie down to the active—- about 500yds. Once had engine quit at 3,000’ with 72deg oat, 55% humidity. Dead sticked it onto Rwy 6 at KCSG. Upon touch down the engine purred like a kitten. Surface temp was low ‘80’s over the asphalt rwy. Couldn’t duplicate it...

In 1991, My wife and I flew a local club Warrior to Mobile for my wife’s cousin’s funeral. Her uncle picked us up at the airport asked me if the Piper had a Continental or Lycoming engine. I was surprised at his knowledgeable question. I replied “a Lycoming “.
He said “That’s GOOD”! I asked why? He replied, “I worked for Continental for 27 years and know what they put into them” !!!
His words, not mine!
Ours was quite noticeably smoother than the 4-banger in the flight school's 172. Get your prop balanced! Never had an issue with ours in 16 years.
Can’t balance the prop...
Sold it 25yrs ago...
Flight schools 172 not a valid comparison. No telling what’s happened to it.
A lot of mechanics (or engine shops) won’t weight match pistons if repairing cylinders. It makes a noticeable difference.