I use only a heavy standard looking pick for guitar whether it is for flat-picking or strumming guitar. The Martin's are excellent and the finely heat-stamped logo enables a good grip.

A thin pick to me is like using a queen of hearts out of a deck of cards.

Finger picking for guitar our banjo, in order to be heard and have fine intonation I feel requires a wide plastic Dunlop thumbpick with heavy metal fingerpicks, one on the index and middle finger.