It really depends on your budget and needs, unfortunately also simply on availability, especially the (3a) series seems to be out of stock frequently.
In general I would say, even the regular (3a) would already provide a solid upgrade over your NP1, although it needs to be said you are losing wireless charging. The kind of downside of the (3a) series: They only get major updates up to Android 18, so the major software support is more limited.
The (4a) series would be the most modern upgrade option, with especially the Pro model offering a premium build quality. They’ll get up to Android 19 in terms of major updates.
The Phone (3) would be the way to go if you want the least compromises and most powerful SoC yet in a Nothing smartphone and don’t want to give up wireless charging. Phone (3) is said to get major updates all the way to Android 20, so if you plan to keep this phone for the next couple of years, this might be the possibly best option.
Personally I think either of the (4a) phones are the way to go at the moment if you don’t care for the flagship, that’s especially true due to the reported stock problems regarding the (3a) series.
