The one that has more seats at the lower price

I know that sounds like a smartass response, but it really is the truth. I flew AB SVQ-PMI on an eticketed ZED, and PMI-FRA now that I think about it. Both flights went just fine (little tight PMI-FRA, but I still made it). I haven't personally been on LH before, but I know that's a very frequently traveled airline for both revenue and nonrev. Can't be that bad.

Take a look at the schedules as well. Come up with plan A, B, and C. Give yourself time to move terminals, if needed. Keep in mind that if you go through another city, you have to look at (and worry about, and pay for) two flights, so if you can get a nonstop that'd be a better choice. I also see that today (as an example) there are 11 flights on that route on LH alone. Plus another 9 on LOT Polish, which I'd bet you have a similar agreement with. Just show up early, and show up often. I'd bet you'll get out on one of those 20 flights, and you could probably see if you can find a free CSA to give you some more information. Or, like I said, start calling their res offices. It's reasonable to ask about maybe 3 flights per call, you don't want to take too much of their time.