Aisleseater

As someone who has been doing Europe as a *G for the last decade and a half (almost all this time as a UA 1K, but more recently as a TK *G), most of it in biz I'd rank current Star Alliance in 3 categories based on soft product, ground service and other issues/punctuality. (All seats are basically the same in my experience)

Category 1 - Best

Austrian and Swiss.

Best soft products in my view. Austrian has the slight edge with food (if that matters) and service IMHO. Both VIE and ZRH have their respective OS and LX flagship lounges and are really nice. And both airports are top class in my view, I think these are the nicest airports in Europe (together with MUC) and both have plenty of top class eating and shopping options if you hit a long layover. I find VIE and ZRH have fewer delays than many other of their equivalents. Also if you do have a long layover, then their are very convenient trains directly from the airport into the city. Also advantage of OS and LX, they tend to be reasonably punctual and are not as prone to strikes as LH.

Category 2 - OK, some good some bad.

Lufthansa, SAS (which in your case are the only two Star airlines servicing KEF), Brussels Airlines and Aegean

Hard products in these are basically the same as Austrian and Swiss, but soft product isn't quite as good in my view.

Downside for LH is that their European network are sometimes prone to strikes or risks of them - and I have been stuck in more than one of these - so you want to keep an eye on this, when you fly with them. Also while FRA is a very solid airport wiith good lounges which I like (contrary to some), and MUC is great on both points, some of the smaller airport lounges are really bad, - there doesn't seem to be a consistency with their product. Eg I flew out of Leipzig a couple of days ago, and the LH lounge (both "business" and "senator " the latter being the supposed better product), was a joke. Only food in the mid-morning were 4 dried sausage slices, which looked like these had been there since the Carter Administration ), and some packaged pieces of pumpernickel along with some sad looking candies, two choices of cereal and stale rolls. The Senator "lounge" was just a smaller room with even less food, although did have some good booze, but at 10.00am I did not partake)

SAS is ok, lounges in CPH and OSL are good, but elsewhere pretty forgettable. The whole airline has come under massive threat from Norwegian, which is a discount airline (itself running into financial issues), but it has dragged down SAS which seems to be competing with Norwegian, has cut costs, and it feels like it. Nevertheless, SAS is a perfectly fine if not great airline in terms of soft product, and both CPH and OSL I find are very efficient airports. (I tend to have longish layovers in OSL so I take the airport train into the city quite a lot).

Brussels Airlines is fine, same as all the rest. Biz is basically Economy seats with the middle seats blocked off with slight better pitch. Unless you're a 6ft+ giant, it's not going to matter. But always avoid the first row, where you often have less leg room. Flagship lounge in BRU is nice, but otherwise it's also an unremarkable airline.

Aegean - I personally like with its connections in Athens into South East Europe and the Eastern Mediterranean. It's a huge improvement on the old Olympic Airlines (which still is operated by Aegean as Olympic Air but which has no relation to the old Olympic other than the brand) which is why Aegean give me a good surprise most times). But unless you have something to compare it with, it's not an outstanding product. Also be aware, that on some flights, like Croatian and LOT, even if you have a business class ticket, on some of the turboprop (and other) services there is no actual business class section/service so be careful which routes you redeem for a biz flight)

Category 3 - Not so good.

TAP, LOT, Croatian

All three airlines aren't great. They'll get you there, but on intra-European flights, you'll wonder why you redeemed points for a biz flight.

TAP (*G) new lounge in Lisbon ok, nothing fantastic but it's only in the Schengen Area - so if you want to go there and you are flying to/from US via Lisbon, it's not accessible as I recall (might have changed), although non-Schengen has separate contract lounges for other Star carriers flying out of LIS (eg for TK which I do use). I also find service on TAP generally below average. It feels like a government majority owned airline which it is.

LOT while it's improved in recent years and I think could get better as they are pitching to be an Asia to Europe and US to Europe relatively low cost connector (like TAP) with some competitive biz class transatlantic fares for instance, they still have a sub-par biz product in my view compared to say OS and LX and even LH in terms of food, drinks and service. The WAW lounge - although it's a big improvement on what it was, is still a bit meh. You can also get stuck on LOT's Embraer jets or Turboprops on key short-haul routes like WAW-TXL, again - not worth redeeming points for biz. Also at least anecdotally, there seem to be an issue with operational delays, and getting stuck at WAW is not that great.

While the new ZAG airport is a huge improvement on the old Yugoslav era one, Croatian Airlines while it has some really good connections into smaller airports in the Balkans like TGD, SKP and PRN, and is now more important than ever because of the collapse of JP and its exit from Star Alliance, the product remains weak. Some of the seats in biz will give you a flashback to travelling in the early 2000s and 1990s and I think even earlier. You get Croatian wines and some rakia selections which are nice, and the staff tend to be reasonably friendly, but the whole airline feels like it has financial issues, which it seriously does. Also it has a very small fleet, I think only 12 aircraft, and wetleases others for certain routes. (Eg earlier this year I got an Air Nostrum aircraft - which is an Iberia (one world) affiliate regional airlines flying on my Croatia Airlines (Star Alliance) SKP-ZAG route! What this all means is that you can get equipment switches fairly often, and delays can ricochet around the OU fleet if there's bad weather, because they simply don't have sufficient planes. And also, the turboprop issue as described above also applies to OU. Having said, this, I'll keep on flying OU because they simply have destinations I need to get to at a reasonably decent price. ) But for redeeming points for a great experience...not so much....)

I'll give a shoutout here to the old JP (Adria Slovenian) which I used to fly a lot and now do miss. LJU is a really nice little airport. One of the perks of JP during connections was to sit on the airport's roof top bar, have a couple of beers and watch aircraft takeoff and land. LH, LX, LO, SN and TK still fly there and frequency of flights for some of these have increased to make up for JP ending operations - so worth connecting if you're there in warmer months.

Hope this helps)