Indexed/Friction. A common question that can only be answered by opinion.

I got a 10sp cassette but only had a 8sp Ultegra set. I ran friction until my 10sp indexed pair came in. I wouldn't go back to friction having run both on the same bike. Just another opinion.

I sold the 8sp stuff on eBarf and ended up only about $25 into the new 10sp parts after it was all over.