The problem with depo is mainly that if you decide you want to try to get pregnant it can take up to a year following yur last injection for your fertility levels to reach what they were pre injection. Also, you have to have it every three onths which can be a problem (also I had alot of spotting whilst on it but each person differs)
have you thought about a coil? I have an ius (mirena) which is a hormonal contraceptive, placed into your womb and it works for 5years. My periods have totally stopped and, other than mild cramping when it was first inserted, it's been fantastic. If you decded you wanted to ttc your fertility levels are back to what they were immediately after removal of it. It's progesterone only so the weight gain isn't usually a problem on po methods.
There is also a non hormonal copper iud, although I don't know much about this as it's unsuitable for myself.