The most important question you can ask if for a list of past customers. As far which system costs more, it depends on what kind of ground loop you are doing.

I agree, past customers are key here! Have them supply phone #s. If they refuse ? answered. as far as cost, Alot depends on your location, water quality(well), sand, clay, rock?(ground)

HI new aboard this site.My question is a race track horrizontal loop 6 circuit 140ft in a trench 150ft 14 ft wide 7 ft deep ok? for a heat load of 35000 and a unit sized at 20,800,sized properly.I'm  being told its at 98 percent,no matter how Ilook at this it can't be 98 percent.Are flow centers adjustable?The last flow center was at 7 GPM ,NEW ONE ADJ. TO 10 GPM, MY UNIT OPTIMUM IS 7 gpm.Also re in 3/4 line 1203,my unit is 2.5 ton. I DO HAVE LOOP PICTURES IF SOME WANTS TO SEE THEM srtourt

Need more information to help with loop size...nature of soil, location, pipe diameter etc. I think an installer who's refrences check out can be trusted there. Many of the installers in my area actually add extra as margin is cheaper than repair. Ask for a referral to a customer where something went wrong. These are my favorite references as it really shows how your contractor responds to problems or complaints. It's easy to impress when everything goes right.
Regarding the 98% question, it does seem counterintuitive, but what it means is that only (about-.... based on a 20 year weather average) 2% of the time will the local temperatures be cold enough, long enough that 20,800 btu's will not do. Some times you might need 2K Btu more, Once in a blue moon 10K more etc. Enough geo to cover the difference may be much more expense than the extra electricity for a resistance coil. Also, unless you work with a 2 stage system, enough heating BTU's may be way to many cooling BTU's. DX or open loop systems have an advantage here as they tend to have about the same heating as cooling output. Closed loop water source tends to be loosely 20% less heating out, so in your area and mine it would be easy to cool to quickly without dehumidifying. You may want to check out a residential ERV to lighten the heat load. Good Luck!
Joe

loop size 3/4 pipe 1680 total feet 6 circuit,in trench 150 ft. 14wide 7 ft. deep.original design loop 745 3 circuit ,heat load 35000,sq,footage of home plus sunroom about 2600 sq.ft.Heat load not done with house plans,wheel used.also g wire not used and 5conductor wire used instead of 8 conductor.in fan only fan will not run,I and think this affects the elec assist that was added in feb.in feb had 15-20 lock outs than assist was added of which no one told me it was being added.my installer called this loop a race track only one headder,and an apr re of 1203 3/4 line and 4638 1.25 line.this loop came about due to diggers not getting to site to find below ground objects.my drop analysis referances circuits in the re of 1203 being low,is 6 to many or what is max?I've had a desuperheater problem since feb in heating and now cooling.it decreasses in water temp. in water tank and heat rate below manufaturer lowest rate.my loop press is 10-3psi in mar flow change serviced to 57-52 psi,this to me indicates a leak,they say its not.press drop feb was 3psi,flow change mar psi drop 5psi,jul 7psi drop,I believe this points to a loop problem and what is 7psi GPM?Also have water flow light in heating and cooling and red led,installer even with low loop press said go ahead run system in cooling.I'm not running system because of 7psi also.srtourt

I would like to help you out here, but I can't quite make sense of your post.

Looks like threads were crossed...
Regarding installer shopping ask to talk to customers where something went wrong. They are my favorite referrals.
The integrity of a company is demonstrated more by how they respond to problems.
Of course you'll want to talk to folks where things went right as well....
J