As far as I'm concerned Paco has got it all wrong...
En cuanto a mi...
I reckon that the best thing to do would be...(inf)
Yo estimo que...
To my mind whaling should be stopped altogether...
Para mi...
I think.../ there should be more help for...
Yo pienso...
If you ask me... / If you want my opinion...(inf)
Si me preguntas a mi.../ si quieres mi opinión...
In my opinion, we should endeavour to...
En mi opinión...
I believe television is a corrupting influence on children...
Creo que...
I feel (very strongly) that more aid is necessary...
Creo (firmemente) que
Personally, I believe...
Personalmente, creo que...
My own view on the matter is that women should benefit...,
Mi propia opinión sobre el tema es...
I am convinced that there is too much violence...
Estoy convencido...