A&C has a good point about fancy aeroplanes!
I've never flown the Robin, but used to instruct on the PA28 - it's an excellent training aircraft. To be honest I wouldn't get too worked up about which aircraft is best to learn in (just not something bonkers like a Pitts), they've all got pro's and con's.
As has already been pointed out, the instructors are key to your progression, I have seen people waste a lot of money on bad instructors. You need someone who you can gel with, you'll probably get an idea of the person during the ground breifing before you've even got into the aircraft. A good breifing will make it seem simple so when you get into the plane you're just going through the exercises and confirming and practicing what you have already learnt on the ground. The only thing you don't want in an instructor is a stress head. These people tend to explode when things go wrong and the situation just gets exacerbated. The best instructor I ever had would call people "dude" and really belonged on a surfboard!
Then there's the question of which airfield to go to. Some people love grass airfields, but as soon as it gets into winter (and sometimes in summer) the field gets waterlogged and nobody can fly. This is just another thing slowing your training and putting longer gaps between each lesson.
On the other hand, tarmac runways are generally more expensive. They also come with ATC and controlled airspace. This can be a mixed blessing since on one hand you're "flying with the big boys" so you've got to be sharp, but on the other hand it's a steeper learning curve. I've met people from grass strips who have licenses but daren't go to controlled airports because they are worried they'll get it wrong or it's too busy. This is a real shame.
And finally, on to the question of theory exams. The majority of the theory (except air law) is very practical. If you take a genuine interest in aviation and immerse yourself in it, asking as many questions as you can, then the exams won't be too difficult. Nothing worth doing is ever easy, but, assuming you've got a modicum of a scientific brain, you should be able to pass with a few hours of study. It is harder than the driving test, but be honest, that was a doddle!