While I agree with sergeant that the 42" hyd is probably a substantial upgrade from the 30" mech, I have to vote for the 30.
My experience was limited to walk behind tillers before I bought my 30-incher. My perception of gardening went through a paradigm shift. Suddenly, carving out a flowerbed 6' wide the entire length of my back yard (200') amounted to little more than a relaxing afternoon.
Sure the hydraulic tiller will make easy work out of untilled clay, but after that first year, I doubt you'll realize the benefit. There is a significant cost difference, whether you're buying new or used. If you're the kind of guy who absolutely has to have the most effective tool for the job, then go hydraulic. But seriously, any tractor-mounted tiller is a pretty varsity piece of gardening equipment. I mean, beyond people who would log onto a gardening blog and spend hours chatting about tractors, the average homeowner would never dream of owning such a thing.
On maintenance: I bought my tiller in absolutely sorry shape. It was rusty, had belts like shoestrings, and had sat out in the elements for at least five years. I cleaned it up, hit it with some spraypaint, greased it up, replaced the belts, and it's done a TON of work for me and my neighbors over the past two years with absolutely no problems. I thught it was pretty odd that Deere would advertise that the hydraulic tiller is quieter than a chain-driven tiller, in Sergeant's quote up above. Who cares? My tiller is a heck of a lot quieter than a mowing deck. I can't imagine why some engineer at Deere even thinks that is an issue.
I should mention in all fairness than my soil is sand, but it chomps through established bermudagrass (originally sodded) with ease. My Dad has the same tiller in the Pocono Mountains, PA, and it definitely takes a bit more effort to process his rocky shale/clay. But after the first time, it's no sweat. I'd imagine that Carbon County PA rocky soil about as demanding as it gets.

So there you have it cjsm, the hydraulic tiller is definitely without a doubt....I mean, the mechanical tiller is hands down....uh.. Get 'em both and then sell off the one you like least, LOL!

Thanks Sergeant and Marineguy for your thoughts!

You both made great points and they are precisely what I have considered. The 42inch will till with ease through my soil but yet after the garden is put in, it may be overkill in years to come. Then again, maybe I could pick up some tilling jobs on the side...;)

Sergeant, how do you move your 42inch about once off your GT?

I'll be sure to post some pictures in the next few weeks to let you guys know which way I went here. My plan is to come to a decision this week.

More comments and pros/cons are appreciated!

I built a dolly basicly out of 2x4 in the shape of a rectangle and about 4inches longer than the tiller itself so I have 2inches of play on either side Once I set it down with the 3point and roll it into the back conner of the Shed.

The 30" tiller has transport wheels built in. It's as easy to move around as a walk-behind mower. Installs in one minute (assuming the deck is already removed).

The 42inch Hydraulic tiller for the GX300 series and X540 has transport wheels built in as well on the tiller sub frame Which I wouldn't have know about because I have the 42inch Hydraulic tiller for the 3point hitch setup same tiller just a diffrent attaching frame and the installation process is about the same as the 30inch mechanical prviding the deck is off. So you would have a easier time then I would moving the tiller around when it is off the Tractor.

Some more questions/thoughts......

42inch hydraulic tiller-

I continue to waffle back and forth here. I guess I am looking for history on whether the 42inch has high maintenance cost and frequent repair. It looks to be a pretty solid piece of equipment. Aside from tine/belt replacements from both tillers, the costly pieces on the 42 inch would be the motor and pump. Any one have any idea on how many hours before these items go "capput?."

My experience over the last 2.5 years is you see far more used 30 inch tillers for sale than the 42inch at JD dealers, Machine Finder or ebay. My thought on this is, probably Deere sold far more 30inch tillers b/c of the higher price of a new 42inch.

Presently, I have found three used 42 inch tillers and no used 30 inch tillers. My dealer will sell a new 30inch for $1400. A dealer about 40 miles away has a barely used 42inch for $800. A dealer in Vermont, about 2.5-3 hours away has a used 42inch for $400 in "like new" condition, he says. I asked him to email pictures before I decide if it is worth taking a look. $400 seem too good to be true, anyway.

I could buy and try out both and then sell the other....no can do. Too much money to begin with and I would take a huge loss in the end!

What to do????? I do know I have to make a decision very soon as I got to get tillin by end of this month!

Thanks

I have had my Hydraulic tiller now for 5 years And I till 3acres twice a Year for that last 5 years and I have not had any problems with it. It still looks brand new From the outside. a little dusty or dirty under the housing but that to be expected. I now people who are still using The Hydraulic tiller on the 1986 JD 318's and the onlu thing the replace was the pump drive belt. Because the hydraulic tiller on the 318 could be driven from either the front or rear PTO on the 318. The maintenance has been low on the tiller. I haven't had to replace any of the tines yet and I have hit some pretty big pecies on concret buried in the dirt. The previous owner of my house was a contractor and he buried alot of garbage around the house from his job sites I found five on machine finder they range in price from $1,300 to $2,000 used for the 42inch hydrulic tiller that will fit your tractor I posted the one nearest your loaction and thats Wisconson the others are in Minnisota and Alberta & Saskatchan Canada

Here is a link that might be useful: machin finder

Can anyone help me find a 42" hydrailic tiller for my JD X540?? Im from Denmark in Europe and I cant get one over here,