Mixed convective heat transfer and pressure drop penalty of nanofluids flow in an isothermal horizontal tube are numerically examined in developed flow region. The study examines three types of nanofluids, simple nanofluids ([Water]/ Al2O3, TiO2, and Cu), Hybrid nanofluids ([Water]/ Al2O3 + Cu), and Ionic nanofluids ([C4mim] [NTf2]/ Al2O3). Richardson number is varied from 0.016 to 2, and Reynolds number is varied from 500 to 2000. The governing equations are solved numerically via the finite volume method by using the SIMPLER algorithm computer code. The computer code is validated by comparing the average Nusselt number with the experimental published data, a good agreement was observed. Performance evaluation criterion (λ) is introduced to evaluate the heat transfer enhancement gain of nanofluid usage to pressure drop penalty at different concentrations of nanoparticles. Results for nanofluids show that the maximum enhancement of the average Nusselt number is 15.5 % for Al2O3 with a concentration of 2% at Richardson number of 0.016. However, for hybrid nanofluids, no enhancement is noticed. Ionic nanofluid results are promising, as the Nusselt number increases significantly (by 37%) with a concentration of 2.5%. Finally, findings of various types of nanofluids investigated in the same numerical conditions are reported and compared.