NERVA has about 250 kN of thrust at 841 seconds of specific impulse.
Merlin 1D has about 1000 kN of thrust at 311 seconds of specific impulse.
That suggests NTRs have around 4x less thrust, but around 2.7z more efficiency than chemical rockets. At a large enough scale craft, the weight of the engine could be considered irrelevant. But for smaller crafts, the Merlin has a thrust to weight ratio of 184:1, whereas NTRs only ever achieved 7:1 (they hoped to get up to around 35:1 eventually).
I imagine the thrust to weight could be substantially improved by making lightweight reactors, but I’m wondering if anybody knows anything about concepts for higher thrust NTRs?
https://en.wikipedia.org/wiki/NERVA
https://en.wikipedia.org/wiki/SpaceX_Merlin
One thing to note is the thrust to weight ratio only matters in relation to some gravity you’re fighting against. It isn’t a thrust to mass ratio. The only time thrust to mass matters in space really is if your burn time needs to be short. If the same amount of ∆V is used, it doesn’t matter if it’s done over seconds or months (or years for that matter). Turning as much of your propellant into as much ∆V as possible is the most important thing.