What is the order of preference of stability for a carbonation .
which is given greater importance ?
No.of alkyl groups or no.of alpha hydrogen???

Sorry student. your question is not clear.
Carbonation is a non-organic process and alpha hydrogen and alkyl groups are related to organic chemistry.

But is most of the organic reactions, alpha hydrogen is more stable.
Because

An alpha H actually has a dual role to play in stabilising organic molecules mainly by :

1- Hyperconjugation

2- Keto-Enol tautomerisation.

You will study further details in higher classes.

Also, Please make sure that question is clear.Then I can help you in a more better way