7018 is a little easier to run and it makes a nice looking bear, but I would go with the 6011 for the following reasons:
1) It has good penetration.
2) It is a fast freeze rod, so it will work a little better on the verticle up sections. ( you want to practice this verticle technique a lot before you do it on your cruiser).
3) It is tolerant of less clean surfaces.
what does it put out,AC or DC(it could be both).depending on that will determine what rods you can use.
ac machines are alitle bit harder to weld with.the arc has a rougher,cruder look to it.and just by nature you have fewer rods that are made to run on ac,7014 and i think 6011 but i'm not 100% sure on those,look at the cans.they will tell you.
dc machines are much better you can use any rod you can with them.
the arc is much smoother.7018 and 6010.(6010 and 6011 are both about the same but the 11 is made for ac current,i think)
are really about the only two rods you would need.
I bit the bullet and took a welding class at the local votec.
It was 2 nights a week for 8-10 weeks, it helped me alot.
Reviewing my notes on rod, the first two #'s (60 or 70) are the tensile strength, the last two #'s are how quickly it solidifies and flux coating. You'll get more slag with 7018 than you would 6011. You'll also get a smoother weld with 7018.
One rod should burn about 1 minute. As for spring perches, I thought you should use a mig welder, so as not to put to much heat into the axle tube. Maybe I learned something in class, if I read my notes right.