250nV at the output between 0.1Hz to 10Hz implies gain, question is how much gain?
Very generally speaking, FET input op-amps have low current noise (this is why FETs are used for low noise amplifiers more often than not as it allows lower noise to be achieved over a broader range of source impedances. See my initial reply).
LT1007 has lower noise. What matters is the 1/f corner freq. not just the volts/root-Hz or advertised output noise volte pk-pk. In all cases, spec sheets are designed to sell parts and play the game of spec-manship to move parts.
http://cds.linear.com/docs/en/datasheet/100737fbs.pdfor
AD797:
http://www.analog.com/media/en/technical-documentation/data-sheets/AD797.pdfDo consider NOT using an coupling capacitor and using a low noise current at the feedback summing junction to offset the DC input as required, Not using the coupling cap avoids a host of problems. With +/- 15 volt supplies, there should be enough dynamic range to accommodate a 10volt ref. given the op-amp has enough common mode range.
Do keep the feed back impedance low as this will go a ways to keep the overall noise low and keep in mind the relationship between feedback loop impedance -vs- source impedance.
Grounding, shielding, overall layout, powering and all those tin details will make or break how well it works regardless of device specs.
Devices in parallel gains a few db in lowering noise with rapidly diminishing returns as the number of devices increases.
Lower impedance generally lower noise, Lower temperature generally lower noise, Lower bandwidth lower noise. For higher source impedances, bipolar input devices are at a dis-advantage.
Beyond this gets into what type of noise aka spectra and a host of other specifics.
Side curiosity, LVA zeners. They are low noise by virtue of their low dynamic impedance, sharp knee at low zener current.
http://ams.aeroflex.com/metelics/micro-metelics-prods-zener-LVA.cfmBernice
Whatever comes out with >= 250nVPP, 0.1Hz to 10Hz and gives a suitable input cap size, is good enough for me for now.
For the OPA140 they have specified 0.5pA input bias & offset. Some quick calculations show that with 1000 ohm Rin and D/C blocking, the voltage noise still outweigh current noise with a large margin; paralleling pays off in this case.