You are being a bit harsh to SkyTeam. SkyTeam airlines are perfectly fine. I find that most airlines are OK if nothing goes wrong, and they are all about equally annoying to deal with if there are any issues like delays / cancellations.

Before SAS 1MM Challenge I've never flown 6 out of 18 active SkyTeam airlines: TAROM, Saudia, Vietnam, China Airlines, China Eastern, and Xiamen. Of the other 12, some of them I've only flown in Business/First, but not in Economy. If anything, most airlines exceeded my expectations. I would definitely fly most of them again.

I didn't have any issues with any of my flights. No delays, cancellations, or any other unpleasantries.

1) Delta F = short domestic flight. FA was a bit awkward, but otherwise the service was very attentive. I was pleasantly surprised. Much better overall experience than on return AA flight.

2) Virgin Atlantic Y = the longest of economy flights. I was dreading the red-eye, but it was VERY comfortable. Nice seats, good recline, good IFE. FAs were friendly. Food was quite decent. Before this I've only flown VS in J. I would fly them again. Top 3.

3) SAS Y = perfectly acceptable. Two short economy flights. Nothing to write home about.

4) Air Europa Y. Quick BCN-MAD on 787. Most of the cabin was empty. I was assigned a middle seat, but my row was empty. Didn't love the amount of legroom - wouldn't want to fly economy across the Atlantic. Business class seats looked comfortable.

5) Air France Y. I usually fly AF in TATL or TPAC business and generally enjoy the seat / service. This was the opportunity to try their economy cabin. It was fine. I hate CDG, so was happy to get out of there.

6) TAROM Y. One of the more disappointing flights, but not the worst. Might have had the empty middle seat. Not a ton of legroom and tiny overhead bins. OTP airport needs a major renovation. This is probably the only airline I would avoid in the future if I have other options. But OTP is not a major connecting hub, so not a huge loss either way. The only flight people clapped.

7) ITA Y. I know ITA doesn't count for SAS Challenge, but they are part of SkyTeam, so I'm including a quick review of them as well. Perhaps, it was the route (FCO-TUN), but wow this was a brutal flight, definitely the worst. No legroom at all, pretty narrow seats, beat up plane. I think I've seen chicken fly in overhead bins. But I might have dreamt the last part. The last time I flew ITA it was still called Alitalia And it was one of my favorite J flights perhaps ever.

8) Saudia J. TUN-JED was disappointing: cold and indifferent service, recliner seat, broken IFE. JED-KUL was awesome: great food, great service, comfortable seat. Tale of two flights. Top 3 flight of the challenge.

9) KLM Y. 5th freedom flight KUL-CGK. Who let the FA dragons on this flight? Old, rude, yikes. I'm glad the flight was so short. I was shocked as usually I've had wonderful KLM flights in J.

10) Garuda Y. Another top 3 flight in my book. I've been pleasantly surprised by GA planes and service on board. Though they still need to iron out some website bugs and IT issues. But I would definitely fly Garuda again, both within Indonesia and internationally.

11) Vietnam Y. Not my favorite flight. FAs were pretty indifferent. One kid tried to steal my seat, another kept kicking the back of my seat.

12) China Airlines Y. Top 5? Quite enjoyable. Nice plane, nice service.

13) China Eastern Y. The website is a mess, but otherwise the flight was comfortable, FAs efficient and helpful. Food edible. Would consider flying MF J long-haul.

14) Korean Y. Mostly flown regional KE J in the past. Y was quite nice. Good plane, smiling FAs. My subsequent KE J flights got affected by the snowstorm, but the airline was quick to refund the ticket. Miles posted quickly, but still waiting for the taxes refund.

15) Xiamen J. Another messy website. As others noted, the lowest qualifying fare class was 3x the cheapest non-qualifying fare. And J fare wasn't much more expensive than qualifying Y. Ended up buying J and loved it. Long day of flying, so it was nice to treat myself. Not sure I would want to connect at XMN in the future, so probably one and done airline for me. But who knows.

16) Kenya Y. Waka Waka. It wasn't as bad as everyone made it seem. Though a random passenger tried to steal my seat, then my friend's seat, then another seat. Not sure what happened to her in the end.