If you had a Pt100 & Pt1000 submerged in water and ice measuring 0°C, the Pt100 would give a reading of 100Ω (Ohms) whilst the Pt1000 would give a reading of 1000Ω (Ohms). The most common type is Pt100 (3-wire), although Pt100 4-wire is still commonly used in labs and applications that require an accurate reading.
A simple way to think about it is that in a Pt100, 1°C is equal to 0.39Ω and in a Pt1000, 1°C is equal to 3.9Ω (100 & 1000 are simply the reference resistance of the RTDs at 0°C) . Our Mineral Insulated RTDs are rated up to 200°C so lets use that figure for our example, at 0°C the pt100 resistance will measure 100Ω (Ohms) with 0.39Ω being added for every 1°C increase.
At 0°C the pt1000 resistance will measure 1000Ω (Ohms) with 3.9Ω being added for every 1°C increase. Therefore if we compare them at 600°C you would see the Pt100 give an output of 313.59Ω whilst the Pt1000 would give an output of 3135.9Ω.
This shows us that the output for Pt1000s is extremely higher, therefore Pt100s are clearly the better choice for accurate readings as it will provide a more accurate and sensitive reading which is ideal for applications that are heated at a slow rate but require in depth measurements, whilst Pt1000s will be more suited to an application where something has a lot of heat applied at once and needs less in depth measurements (e.g rough figures such as 67°C, not 66.72°C), It is also worth noting these factors can be dependent on the wire configuration used.