At each tier of logs, crossbow stocks seem to give the highest XP for some reason. At higher tier logs, It is advised to craft Shortbows until you have the level for the crossbow stocks and then make those until the next tier of logs.
1-20 > Shortbows - around 35 logs
20-35 > Oak shortbows - around 43 logs
35 -> 50 > Willow shortbows -around 92 logs
50 -> 54 > Maple shortbows - around 39 logs
54 -> 65 > Maple stock- around 198 logs
65 -> 69 > Yew shortbows - around 126 logs
69 -> 80 > Yew stock - around 680 logs
80 -> 85 > Magic Shortbow - around 591 logs
85 -> 92 > Magic shieldbow - around 1377 logs
92 -> 99 > Magic Stock - around 2519 logs
All of these numbers are on regular xp.
For training until 65, i would suggest obtaining logs by simply cutting them as it will be faster than trying to buy from other players, usually nobody has these logs in the bank, they aren't common in pvm.
For Obtaining yew logs, you can either cut them, buy them from other players or kill araxxor for them. Araxxor drops them very commonly and as a result many players may have upwards of 10,000 yew logs in their bank and not even need them.
For obtaining magic logs i would suggest either buying them or doing rise of the six. Rise of the six drops magic logs very commonly and is an easy boss, there is a guide for that also on these forums. I would not suggest cutting magic logs as they are very slow to cut.
Apologies for no pictures, fletching is a very dull skill and i didn't need to illustrate anything.