There are some magazine articles on this that you can search for, some have comprehensive discussions of the benefits and risks of a buffer. To boil it down as far as I understand, you would avoid having a buffer in front of vintage style pedals with germanium transistors. These would include a Dallas Rangemaster, Tone Bender, or Arbiter Fuzz Face. The germanium transistor driven fuzz pedals interact magically with your guitar's volume control, and they clean up as you roll back the knob on your guitar. If you put a buffer between the guitar and this type of pedal you'll sacrifice this function.
Another issue is how different pedals interact, for instance if you want your wah pedal in front of the distortion pedal (I think having distortion before wah gives you a wonky seventies x-rated movie soundtrack feel that's not always what I'm looking for, so the wah before fuzz or distortion gives a more agressive sound, but hey who makes up these rules). OK anyway, if you like the effect of the boost from the wah going into the fuzz then you don't want anything with a buffer in between them.
Otherwise, a buffer is a really good thing to have, considering that a pedalboard is like adding another twenty foot cord between the guitar and the amp, not to mention the cord going from the board to the amp, and things get dull going such a long distance to the amp. A unity gain buffer gives more punch and clarity to the signal and it's basically part of any modern pedal circuit. The Boss tuner that you see on almost any gigging musicians pedalboard has a buffer in it.
SO, unless you've got germanium or unobtanium pedals, you would put the buffer early in the chain to drive the rest of the length of cabling and effects. This might help cut down on noise as well. I found for instance that the Boss Tremolo pedal was noisy on its own but tolerable with a buffer in front of it.
Also consider that quality cables will make a difference here. Do a taste test with Mogami, DiMarzio, George L's, or Planet Waves and they'll come up ahead every time against the store-brands (notice how I didn't push "Monster" cables?).
Also in terms of the general order of pedals, a delay might work best later in the chain; if you put it before the distortion then the lower volume trails/repeats will get cleaner as they decay which is wierd. I like to think of trem or reverb as being amp effects that come after everything else. Chorus before distortion sounds grating to me, but after is fine. Same thing for Leslie, phaser, or Univibe modulation effects, better towards the end after the distortion or boost pedals.
OK your question was simple and my answer wasn't. Put the buffer as early as possible but don't put it in front of a Fuzz Face.
Generally, you want a buffer as close to the start of your chain as possible, given that it has the right input and output impedance, to retain your original signal, as once it's lost you cant get it back...
as most pedals with buffers all differ, and don't all play nicely with each other, there are no hard and fast rules here... the best thing to do would be to get a pedal that is a dedicated buffer pedal and move that around among your other pedals and see what you like.
having said that traditional fuzz face circuits *and others* dont like having buffers before them, so in your case you probably wouldnt like sticking your buffered delay at the start of your pedal chain! but then again it's all subjective...