The main difference is duration of action / half-life, with frequent injection such as Billegitimate's letting propionate work very well, and cypionate and enanthate still being injected preferably at least twice per week.
The other difference is that in this particular drug class milligrams are reported in terms of total weight rather than amount of parent steroid contained, so (for example) 150 mg/week of testosterone propionate does contain a little more testosterone than 150 mg/week of enanthate or cypionate. This however can be completely compensated for with dosing, as mentioned.
I don't think there are any differences in conversion to estogen.
It could well be, as a fine point, that an individual does better with a fluctuating pattern as per Billegitimate's thought. For most, two or more injections of enanthate or cypionate per week is a perfectly good way to do it.