I've been evaluating both (kysely, drizzle), and I'm leaning towards Kysely. Drizzle is the latest, but both are moving fast if you look at the git insights. I find Kysely more enjoyable and straightforward -- intellisense autocompletions work better (for me at least), and the expression builder combined w/ helper methods like jsonArrayFrom offer a lot of flexibility over how to shape the output, so you're in full control, which is one of the reasons I wanted to explore alternatives to primsa in the first place. I had actually decided on kysely, but am taking another look at drizzle because of recent support for relations added. The added support is a nice addition, but there's boilerplate one needs to write to take advantage of and, frankly, I just find it easier to get same results w/ kysely, again, w/ added flexibility (it is not trying to be an orm). Some things I really like about drizzle are not needing to generate schema and lets you map column names (e.g., created_at db col maps to createAt object name). Drizzle can also infer types from schema, but, I haven't found this to be a big pro relative to kysely because 1) it takes very little effort to build a zod schema that "satisifies" the kysely type definitions and 2) I'm overriding the drizzle inferred types anyway to get the finally runtime checks implemented (e.g., is a cuid2 of 16 len, not just is a string). I've also been using prisma-kysely, which gives me ubiquitously supported prisma tooling for handling migrations, etc.
edit: while not exhaustive, I'm seeing better perf (by about 20%) using kysely compared to drizzle for identical queries on planetscale. Take this with a grain of salt since I've made no attempt to measure exhaustively, or optimize -- just using "as-is" so to speak, but thought it would be with noting and nothing to indicate to me that drizzle offers big perf improvement over kysely as has been suggested. Thanks for this post btw. Drizzle is hot and shiny right now (Theo just promoted big time), but after taking a second look at drizzle and in the process of writing up my thoughts here, it's become clear to me that I'm sticking w/ kysely.