our preference is for jute which is soft but sturdy, or hemp, hemp can be a bit scratchy if you're not used to it but you can prepare it by soaking it in boiling hot water for around 5 hrs then after thouroughly drying apply a good coating of bees wax (some use baby oil though i wouldnt recommend it) to smoothen it and help loose the 'smell' which not everyone likes, it also gives it a longer life span although i wouldnt recommend over use of it. (the sisanal or manilla type is not particularly usefull for bondage though) you can get it pre-treated and in various colours if you look around although im a bit dubious as to its quality.
we prefer it as it is ....totally natural.
a lot of westerners use synethetic rope such as nylon, propyaline,and cotton.cotton is ok its comfortable certainly needs no preparation other than finishing the ends so it doesnt fray.
it leaves some lovely marks and you can get hold of some very pretty colours if thats part of the attraction for you,but you need to be careful when choosing it as it can be a bit too pliant and stretchy especially for suspension, again it depends what kind of ties harnesses etc you're opting for.
it's also very easy to find in all the diy stores and is generally on a roll where you can measure your chosen length.
check out the plaiting or twist too 3 strands is better than 4 (in my opinion) and plait leaves lovely patterns but with man made materials twisted tends to be slightly firmer slightly less 'stretchy' and longer lasting.
westerners tend to use longer lengths often around 26-30 feet but it's more likely to get messy twisted and become more difficult to keep control of when applying it and you can often find yourself wondering what to do with the surplus length coiled around your lounge!
if you take a look at most japanese Masters work you'll find they use smaller lengths around 20-23 feet and simpler less intricate ties.
try sticking to simple knots such as larksheads, overhand etc its safe wont slip and can be used for most harnesses etc.
in fact many harnesses and such can be done with no ties.
a width of 6 or 8 mill is best and the usual choice for most people, some use 10 although i've found that that can be a bit too bulky and more akward to handle and look crude it also makes it more difficult to loop, 4 mill which is rarely used can dig into and nip the skin and can be a bit unpleasent although its good for practising nipple work.
of course this is going by what ive found and my preferences as with anything you need to learn through your own judgement and practise but keep researching bondage can be dangerous and you need to be up on some basic knowledge of the body too and consideration of room temperatures, health,tiredness (the rope bottom in particular) any breathing problems such as asthma recent colds etc before you begin. i dont mean to sound patronising sorry! but sometimes people want to jump in quickly and overlook the little (or what can be turn out to be not so little) things like that.