Colour, Slides Or Black & White?

35mm & 120 film come in a variety of flavours! All different brands and types produce different tones, colours & contrasts! 

Colour Negative: 

This is your standard colour film. It goes through C-41 processing, giving you a set of negatives on your film after development! These are then scanned & inverted by the photo lab, giving you a set of usable prints to show off! They have a range of different ISO's from 50-1600! 
Examples are: 
Kodak Gold
Fuji Superia
AGFA Vista
Kodak Portra

Slide film: 

This is a type of film that gives you a set of positives on your film using E6 processing! These can then be mounted in cardboard, and projected onto a wall to show off! Slide film typically has a lower ISO value, which means sharper grain and colours! Slide film tends to have a more 'natural' tone to your photos, and features whopping contrast to knock your socks off! 
Examples are: 
AGFA CT Precisa
Fuji Velvia
Rollei Crossbird
Kodak ektachrome

Black & White: 

There is two types of black and white around! 

True/traditional: 

The original black and white film! It is developed in a darkroom using developer, stopbath & fixer! Prints used to be done by hand using special paper and an enlarger! ISO's range from 50 - 3200 iso! 
Examples are:

Fuji Acros
Kodak Tri-X
Ilford HP5

C-41 BW: 

This is a type of film that is developed like a normal colour negative film, but produces black and white prints! Sometimes the scanning can give them a sepia tone, but if this doesn't suit, you can scan your pictures and adjust them digitally. This is a handy, cost effective way to shoot black and white photos! ISO's are usually around 400 iso. 
Examples are:
Kodak BW400CN

Ilford XP2