Just my personal opinion, and bear in mind that I normally don't have sets that deep, is the 2-HP 10 GPM pump.
You only include the total rise for head, from pumping level to final elevation. Your horizontal runs do take up some of the "head", but the amount usually is so small that you can mostly ignore them. Every ft of head takes approx. .4 psi, whereas pipe runs usually take hundreds of feet to take 1-2 psi from the total. Make sure you use big enough pipe to create the least amount of head loss.
For what you're needing it sounds like you need a pump in the 10-20 gpm range. Unless you're doing a lot of watering for the lawn, the 10GS20 will give you about 13-14 gpm at ~50 psi. If the water level drops to say, 300 ft you're still at 10-12 gpm at ~50 psi.
If you go with the 13GS30 you're at about 16-18 GPM at 260 ft of head. If the water level drops to 300 ft you've still got 15-16 gpm.
Both drillers are right and both have their opinion. I'm not sure what kind of pipe they're planning to set the pump on and it could make a lot of difference in the cost. Normally around here we use sch 80 pvc with stainless couplings but I have found that materials vary from place to place. I don't normally use 1.5" pipe, I go with 1", 1.25", or 2". If you go with the 10GS20 I would go with 1.25" pipe all the way to the pressure tank/house. If you decide you need the extra 5-6 gpm then I would upsize the pipe, but it would still be OK to use 1.25" pipe. You will lose a little flow staying with the 1.25 pipe though. Also, when you go with the bigger motor/pump you will probably have to upsize the wire. I don't have a wire chart in front of me at this minute but that might make a difference in cost.
If you decide to go with a conventional system I would recommend going with a well-x-trol tank that will give you at least 1 minute of run time. So in addition to bigger pipe and wire you will need to go with a bigger tank if you decide on the bigger pump. You just have to decide what's best for your needs. If you go constant pressure route then you could use a smaller tank.
Personally I find that most people can easily make it with a ~10 gpm pump as long as they're not running the bath, dishwasher, washing machine, filling the pool, watering the grass, etc. For normal use it will be plenty. If you find yourself watering the yard more than occassionally, you may wish you had went with the bigger pump.