Transfem

I can't speak for others but I hate needles. So, the advantage of pills for me will be that they aren't needles.

I do injections because I’ve heard it’s easier on your liver (or maybe kidneys I forget exactly ATM). It also has a higher absorption rate, and as a monotherapy I like not having to keep track of multiple medications.

I hated needles prior because of some traumatizing OD deaths in homeless camps (I kinda made it my litmus test to see how much I wanted HRT), but after about 2 weeks my anxiety was gone, and the benefits far outweighed the momentary ick of stabbing myself with a needle.

Injections all the way. (I am not trans, but I'm familiar with TRT protocols).

First, injections are easier to dial in blood levels. Pills may not come in the doses you need, and may not be readily split. It's fairly easly to add or subtract 1mL with depo estradiol; if you needed to, you could even dilute it to get finer control, but that's best done by a compounding pharmacy.

Second, pills tend to be hard on your liver. I know that, in the case of anabolic androgenic steroids (AAS), they're methylated in order to avoid first-pass metabolism by the liver. Methylating is necessary to allow them to act properly--if they're matabolized by the liver, then you get none of the therapeutic benefit--but methylating makes them really harsh on your liver, and can, in extreme cases, cause cirrhosis. (That's much more common in body builders that are taking massive doses of drugs, rather than people that are taking them under the guidance of a doctor. Buuuuuuut one of the potential serious adverse side effects or oral estradiol is jaundice-yellowing eyes and skin--which indicates potential liver problems in some people.)

Last, pills are generally a daily or multiple times daily dose. Biological half lives of oral medications tend to be under 12 hours (unless there's some XR version that I'm not aware of), so missing a day can significantly affect your hormonal levels. Injections--like estradiol cypionate--have a biological half life of about 5 days. If you inject weekly, you quickly end up building to a fairly stable blood level.

I believe that you have steadier hormone levels when you take pills twice a day, vs weekly injections. I don't think that makes a big difference practically. I only have experience with pills because I also hate needles haha

As someone else mentioned, the pills can be harder on your body. I switched to shots and have no regrets. Anecdotal but my body was just not absorbing the pills well and I always battled to get my hormones right. It's been much easier to do with shots.

I used to be on patches (until they became hard to get), not pills, so I can't really compare, but I have observed that since I started injectable E, the effectiveness has increased noticeably.

That said, at least here in Queensland, the availability of prescriptions for injectable esters other than valerate here is next to impossible, and even then convincing your doctor to prescribe valerate is really hard.

Injectables are easier and cheaper to get diy, so I use them. I was a bit afraid of needles, but that anxiety quickly faded. Monotherapy is also a nice bonus, compared to having to buy and remember extra medicine.