UTAUT vs TAM, which one is better to use ?

They are just different. TAM is mostly individual level (but may be applied to org settings as well) and UTAUT is org level only.

hmmm

In my opinion UTAUT is more recommended to use, since it is developed through a review and consolidation of the constructs of eight different models (theory of reasoned action, technology acceptance model, motivational model, theory of planned behavior, a combined theory of planned behavior/technology acceptance model, model of personal computer use, diffusion of innovations theory, and social cognitive theory ).

Look at UTAUT 2 as the latest version of technology acceptance models.

I Agree With Danial Jahanshahi

Going back to basics. Read Venkatesh et al.'s (2003) seminal work that established the UTAUT. Read it critically and you will see the excellent research methods that proved the following and endure to this day.

Over time, it seems researchers that attempted to add to the model in various contexts and study designs, only reconfirmed various findings of Venkatesh et al. (2003). Holden and Karsh (2010) found that few studies in their literature review evaluated the four moderators inherent to the performance of UTAUT. For example, Dwivedi et al. (2019) aimed to revise the UTAUT via meta-analysis and structural equation modeling of data from 162 earlier studies. They found that attitude to statistically significantly predict intention to use while moderating the effects of the four key factors. However, Dwivedi et al. completely dismissed key findings and the moderators which were proven essential in Venkatesh et al. work. First, Venkatesh et al. found attitude, self-efficacy, and computer anxiety nonsignificant toward predicting user intention; however, each was fully absorbed through performance expectation and effort expectancy. Second, Venkatesh et al. found the following three contributions of the four important moderators in the UTAUT. First, age, gender, and experience affected the strength of the relationship between performance expectancy and user intention. Second, social influence is affected by all four controlling factors but nonsignificant without them. Third, facilitating conditions significantly predicts usage only when age and experience were accounted for in the examination of that relationship (Venkatesh et al., 2003).

Dwivedi, Y. K., Rana, N. P., Jeyaraj, A., Clement, M., & Williams, M. D. (2019). Re-examining the Unified Theory of Acceptance and Use of Technology (UTAUT): Towards a Revised Theoretical Model. Information Systems Frontiers, 21(3), 719–734

Holden, R. J., & Karsh, B. T. (2010). The Technology Acceptance Model: Its past and its future in health care. In Journal of Biomedical Informatics (Vol. 43, Issue 1, pp. 159–172). https://doi.org/10.1016/j.jbi.2009.07.002

Venkatesh, V., Morris, M. G., Davis, G. B., & Davis, F. D. (2003). User acceptance of information technology: Toward a unified view. MIS quarterly, 425-478.

TAM is a subset or rather a component of UTAUT

TAM is one of the eight building models to form the UTAUT model: I do recommend you to read the article of pioneer, Venkatesh: USER ACCEPTANCE OF INFORMATION TECHNOLOGY: TOWARD A UNIFIED VIEW

Alexander Serenko Can I get the reference journal / book?

I have the same question as yasser

I suggest you read this paper:

Venkatesh, V., Morris, M. G., Davis, G. B., & Davis, F. D. (2003). User acceptance of information technology: Toward a unified view. MIS quarterly, 425-478.

UTAUT and TAM both are model serves for individual acceptance and organizational acceptance over the IT components by theory of reasoned action, technology acceptance model, motivational model, theory of planned behavior, a combined theory of planned behavior/technology acceptance model, model of personal computer use, diffusion of innovations theory, and social cognitive theory

I found this article that might be interesting:

Rondan-Cataluña, F.J., Arenas-Gaitán, J. and Ramírez-Correa, P.E. (2015), "A comparison of the different versions of popular technology acceptance models: A non-linear perspective", Kybernetes, Vol. 44 No. 5, pp. 788-805. https://doi.org/10.1108/K-09-2014-0184

l'UTAUT est plus général que le TAM