title says it all. I was trying to land a small probe on duna today, but every time I just failed. and after this happened several times, I thought, 'why in the name of jeb am I going to duna.' I thought this once I realised that duna Is probably the hardest atmospheric body orbiting the sun to land on. this is for a couple of reasons:
1) it is the smallest atmospheric body orbiting the sun, meaning it has a small sphere of influence to aim for, meaning that you need the phase angle to be almost perfect and you could waste precious fuel making correction burns since you have a small window of time and delta-V to aim for. because of this I eventually had to resort to mech jeb phase angle readouts to get the correct time.
2) Ike. it even says it on the Ike description. ike is in the perfect place and is the perfect size so that most times you will get a encounter with the troublesome moon. What's more, is its coin flip nature of the gravity assists it gives you. it can either leave you on exactly the same path you were on before, or try to fling you off back in to interplanetary space meaning you have to spend even more DV cancelling that out.
3) this is the thing that finally caused me to rage quit trying to land on duna. its extremely thin atmosphere. unfortunately, duna has an extremely thin atmosphere. this means a lot of things. aerobraking requires you to go deep in to the atmosphere, parachutes may work however they will barely slow you down and in my experience just cause more problems than they solve, as you will still crash ans explode without engines, and you will have very little time to make the burn required when landing to stop yourself since you still going at considerable speed.
overall that is why I think that duna is actually harder to go to than eve and even Jool in some respects. eve and jool both have nice, big SoI's to aim for, thick atmospheres to aerobrake, and in eves case parachute land with, and no pesky moons to throw your orbit off course (yes jools got 5 moons, but these are quite spread out and are mostly all small so they are easy to avoid.