Many people wonder what markers they should buy, I will try to answer this question from my own experiences and knowledge. First, if you are looking for a nice marker that will give you a nice constant drip I recommend the Oink Mop that can be found on this website:
The mop costs only $2.50 and will last for a pretty long time. The ink is also very good because it is very permanent and also very inexpensive.
On The Run (a.k.a. OTR) supplies great markers for low prices, the Hard To Buff models are very resistant against all the elements that your art might go through.
If you would like me to give you my opinion about a marker leave it as a comment, thank you.