Vespa looks pretty compelling; indexing looks like a dream.
I'd recommend basically anything else over a customized ES / Solr cluster. Some of the least fun clusters to manage. Great for simple use-cases / anything you see in a tutorial. The moment you walk off the beaten path with them, best of luck.
Solr has its quirks for sure, but I’ve seen multi-terabyte sized indices running with great relevance and performance. I would call it a mechanics search engine. It is very powerful but you need to get your hands dirty.
I'd recommend basically anything else over a customized ES / Solr cluster. Some of the least fun clusters to manage. Great for simple use-cases / anything you see in a tutorial. The moment you walk off the beaten path with them, best of luck.
Just an anecdote