OMFG, this too! There's an app that samsung preloads called peel remote. it's for their IR blaster that works with tvs stereos etc. but as of a few months ago, they started putting full screen ads in. and not just in the app, the damn things pop up randomly when i'm using the phone. like, with no warning, a random ad will take up my whole screen. Even when i haven't used the app in MONTHS! I finally disabled it and uninstalled all the updates. I really like the app itself, when i actually use it. It's really well made, but it's like they just decided to monetize their whole install base one day and put these ridiculous ads in.
Also, i haven't had a motorola in years, so i guess i shouldn't comment on it. they could be better now, but they used to be cheap and break all the time. What kind of mods do you do to them?
EDIT: i wish i could just pay samsung like $10-$20 and get a clean install of android for my s6, or at least be able to remove preinstalled apps permanently. or better yet, i wish google would just offer android directly for third-party phones. the popular ones at least...