If you are from Europe I suggest German ones … they work really well for me… generally selecting the ones closest to you may also help … I had an issue because some engines has a really long response time and sometimes by waiting for them the search drops giving you an error I keep google Bing qwant and DDG works out great as everything on these days u have to give up comfort and ease of use for privacy…
I suggest searching the topic online I’m not an expert but I guess that searx makes the researches for you and comunicate the answers back … so it’s at least adding a step in between… Also I heard that DDG was taking a less open and clear politic about privacy witch definitely did help me chose to switch to searx