See if I'm honest I'd give them both up to win the Europa League
No way.
I'm fully aware the Europa League is a great tournament and it's currently way over our punching weight (look at the last winners: Atlético, Man Utd, Sevilla and Chelsea, all far ahead our financial standing).
However, who really remembers Europa League winners ten years on?
What does winning the EL mean? Are you the best European team of the season? No. The second best? We all know you aren't. There's an argument for 17th. It's a very nice achievement. But that's really all it is.
Atlético have won it 3 times, but their European standing truly comes from having won La Liga and getting to two Champions League finals. Zenit have won it. Are Zenit a relevant European side? Are Schalke? Or Göteborg? Or Borussia Mönchengladbach?
No, they are not. We already are in the only truly relevant list of European winners. We've got the big ears. And we got to a second final. And then to a UEFA Cup final not that long ago, yes. The EL wouldn't change our CV that much.
10 in a row is something that no team in the history of Scottish football has ever accomplished. Not Jock Stein's team, not the 90's Rangers. It probably won't ever be done if we don't achieve it now. That's why (and since we've already won a Double Treble) I'd take it over a 3Treble at the moment. And definitely over the EL.
I'd take the EL over another treble now, though. But we're not winning it anyway, so...
EDIT:
I want to celebrate winning number 8 properly only been done once without cheating, so give it the huge credit it deserves. Potential league wins 9 + 10 will be incredible if and when achieved but bin all talk of 10 like it's a foregone conclusion. Doing 8 is ALL that matters right now
Also this. 1000 times this.
We haven't won 10 in a row yet. There's no guarantee we will. There's no guarantee we will get 8. It's gonna be a long, grueling way. We have to give our competitors the respect they deserve and earn it game by game on the pitch. And if we don't achieve it, we have to value our 7-in-a-row as the amazing achievement it is on its own.