Mine was the HGCE Dagger L. I still haven’t seen the series it came from, but it’s a really nice kit. Looks nice with no need for paint or stickers (although I did end up putting a bit of paint on it eventually.)

My first kit was the High Grade Gundam Age-1 Normal. Nothing special really, but fun to build. As for what I’d recommend: either a suit you like from the anime, or just one you like the design off.
and a Tip: the newer the kit, the better it (usually) is.