Sears Diehard Gold or Mercedes orginal battery
 

For about the same price what should I get for a replacement battery for my ML320 year 2000.

Sear Diehard Gold (not the AGM, AGM more expensive) or Mercedes Original Battery.

Which is the better batteries.

It is hard to believe those are the same price, but my vote is for the OEM battery.

Hard to argue with an OE battery for the same cost as aftermarket, but still I'd compare the specs and warranties on both and also consider which is more convenient should you need service in the future.

With all the Sears closing down, that may be hard to predict. I had a Die Hard Platinum AGM finally die on me that I bought in 2010. Still had a bit of warranty on it good for $30 off a new battery.

I bought an OEM for my car (a '98 diesel) last year. The previous OEM had lasted a few months short of 9 years. The price was better than prices quoted by Auto Zone and Sears.

I would get any decent battery from the most convenient location to my house. Dealers have proven difficult to work with if warranty exchange is needed (as in "you have to bring the car in first." "But the battery is dead!", "Rules is rules.") OEM are now Interstate batteries anyway, to my knowledge.

Interstate. To-bad costco does not carry this size. If so it would be 50% off. They have it on their website but they don't carry it in their stores (at least the stores in Northern California)

For the record I bought a Duralast and it is working fine.

I lucked out. This car had a 1 y/o Duralast AGM when I bought it.

At one time, Costco carried a brand of battery labeled Kirkland. They were all the rave on the web.
They have since been replaced with a brand simply labeled Interstate.
I have bought and returned more of these newer Interstates than I care to remember.
There is a reason why they are cheap.

Both of those brands are made by others, as are the Mercedes and the Sears and the Duralast... The only actual battery manufacturers in the US that I know of are Johnson Controls, US Battery and Trojan. There may be some others.

The good old MB brand, Hoppecke, was bought by Varta 10-12 years ago and is no more.

To the best of my knowledge Interstate makes batteries for MB.

x2 I've replaced more Costco Interstates than Duralasts or Walmart's value line (ValuePower?) within the prorated period. At least it's quick and painless at Costco.

Are non-Costco Interstates better? Does NAPA sell good batteries?

Sixto
98 E320s sedan and wagon

I stopped buying Interstate due to price.
I buy Bosch Premium Perf fom PoopBoys and I always find they have a rebate so I end up paying a tad over $100 for a group 49 with a 60 month warranty. I had a bad Bosch, it would lose charge about a year after I bought it and they replaced it at no pro-rated fee, thats a good warranty!
Local dealer wanted $150 after they gave me some sort of discount because I complaied over their initial quote.
DDH

Roger any battery of the correct size/group. In the case of a diesel, I would opt for the highest A/H capacity.