The professional view is as follows
You can do as good a job with a manual brush as an electric one if you know what you are doing/ have good dexterity/ are a dentist but the evidence is that the average person does a better job with an electric brush.
You still need to floss / use little brushes between the teeth whatever brush you have.
The brush should have a small round oscillating/reciprocating head – I.e. twisting back and forth not just vibrating or spinning.
The Braun / oral b brushes are the best – better than sonicare/ Colgate etc
You don’t need to spend a fortune. Middle of the range Braun will be fine – they invented a great basic concept years ago then have had to come up with lots of bells and whistles to keep coming out with new models. You don’t need a wireless timer etc.
Sainsburies boots etc often have them on sale