I am going to compare the the best known audio-depictions of Merry and Pippin: the three movies directed by Peter Jackson (on the assumption that it is the director who chooses the accent which actors adopt); the audiobook of Lord of the Rings read by Rob Inglis; and the BBC Radio drama-adaptation by Brian Sibley - directed by Jane Morgan and Penny Leicester.
In the movie, Merry is given a mild 'Mummerset' accent - which is what actors call the generic West Country rural accent, characterized mainly by an exaggerated 'r' sound. This same West Country accent is adopted in a more extreme 'Ooh Arr*' version by Sam Gamgee, in all the versions here studied.
Probably to provide a distinguishing contrast, the movie Pippin's accent is mildly Scottish (the actor comes from Glasgow).
In the audiobook; Rob Inglis gives both Merry and Pippin a Mummerset accent; the two hobbits being distinguished mainly by the timbre and pitch of their voices.
But in the BBC drama version, Merry and Pippin are given an English upper class accent (with Pippin having a lighter and younger-sounding voice) - and they are depicted as a couple of young 'toffs', rather like PG Wodehouse's Bertie Wooster and Bingo Little of the Drones Club.
(BTW, the BBC radio actors were Richard O'Callaghan as Merry and John McAndrew as Pippin.)
And this is the most accurate in terms of Merry and Pippin's very elevated position in the Shire Class system. Pippin is the heir to the Thain, which is the King's representative in the Shire; and therefore the nearest Hobbit equivalent to a young prince. Merry is heir to the Master of Buckland - which is the Shire's semi-autonomous outpost; and therefore something like the heir to a Dukedom.
At any rate, Merry and Pippin are the two poshest young Hobbits in the whole Shire!
So, full marks to the BBC Drama for getting it right, and commiserations to the other contestants.
Note: I was myself raised in the West Country - Devon and Somerset - and can confirm that the rustics in that corner of England really do say Ooh Arr - with remarkably frequency.