Delivery methods are all ultimately the same. E goes in your blood and binds to cell receptors that tell them to behave in a certain way. If you're on transdermal because your Endo says that's what you should be on, then that's what you should be on. I've read that people over 40 and smokers are often put on transdermals because of lower risks. If you're in your late teens ethinyl estrodiol can be used safely in pill form, if you're over about 25ish estrodiol valerate is fine in pill form. I don't know anything about implants or injectables as they're not used where I'm from. The reason they say for this is, if something starts to cause a problem, you can fix it by stopping taking the pills, but you can't "un-inject" something once it's in there.... You have to wait it out.. Precautionary principle and all that..
As for implants, I'm not sure if they're funded. I've heard they're very popular with endo's treating transsexuals in Australia though. I'd quite like to give implants a go personally.