5.3 vs 6.0: which LS should I swap?

5.3 (325 ci): the most plentiful LS engine; 3.780 in bore; 270–320 hp stock depending on version. Iron (LM7, L59, LY5, LMG) and aluminum (LM4, L33, LH6, LC9) versions exist. Speedway Motors calls the 5.3 the default choice for most swaps: cheap, everywhere, and reliable.

6.0 (364 ci): 4.000 in bore; 300–361 hp stock (LQ4, LQ9, LY6, L96 are the common truck versions). More low-end torque and more room for boost, a bit more expensive and usually iron.

Pick the 5.3 if…	Pick the 6.0 if…
Budget is tight, lighter car, mild build	You want more torque, heavier vehicle, or boost
You can find an aluminum 5.3 (L33/LH6/LC9) for weight savings	You want LQ4/LQ9 bottom ends for turbo builds

Swap parts (mounts, pans, accessory drives) are the same between them; the bigger differences are heads, compression and ECU generation.