Well, patches are the recommended method for cis women who want a steady, constant level of estrogen; it's something the patch makers advertise. (I mention cis women because, as always, the majority of research has been done on them, and the US FDA is approving those ads - whereas HRT for trans people is generally "off-label" use.) Vivelle at least also claims that the patch requires the least estrogen *administered* to achieve the same blood levels, but I have no idea if that's true, aside from the likelihood that the FDA might intervene if it weren't.
Cis women don't do injections, I believe, but everything I've ever seen suggests that those cause a spike in E on the day of the shot that slowly declines until the next injection. Higher levels at first, possibly, but definitely not steady.