Spirals would be perfect! Whenever you have straight lines, you want to use curves. My favorite for a log cabin is the Baptist Fan, because of all the curves. Please show your progress!

I like the suggestion of Baptist fan. I understand your hesitancy, as I just completed the quilting on mine...quilt has been in progress for at least 5 years.
I think you should start on the dark sections with feathers in a thread color that will blend in. By the time you are ready to quilt the light sections, you will be an expert! :)

Wow, your quilt is pretty! And your advice is great.

First - and I think most important - it is your quilt! Whatever you decide is the correct decision. Having said that, if you are not comfortable with your feathers and afraid you'l 'mess it up', this might not be the top to practice on. Do something a bit more simple and let the log blocks stand for themselves. Perhaps a spiral in a few of the logs of each block. It does not have to be an allover pattern unless you prefer the squashed down look. Or, depending on the layout, perhaps a diagonal running thru the whole top. I'm sure it will be lovely no matter what you decide.

I quilted a log cabin with circles and loved it.

Can you post a picture of it so we can offer specific ideas? With it so large, you can do various motifs in different sections.

I really understand your hesitation. I procrastinated long and hard before quilting my sister's LC quilt because I wanted it to turn out very well, but I lacked skill. However, I wanted to put things in it that would make her smile and would enhance the theme. The theme was love of horses. (It also helps that she lives in a log cabin in Kentucky!)

In my layout, I had a lot of negative space, so I planned one motif (horse head I free-handed on paper till it was right, then cut it out and then made a template, surrounded by a circle made from a paper plate)---for all of those matching spaces. I also free-motioned a rope/lasso/loop-de-loop design, plus some channel stitching, big horse shoes, etc.

Use this quilt as an opportunity to improve your skills. Don't stay stagnant. You will get more and more confident. As the Quilting Marine says, "it's only fabric and it's only thread." Do one section at a time, and stop when you get tired or flustered.

135 x 135 Holy Cow! That is a large quilt to tackle. I would do something that I would feel comfortable with. The stress of not having it turn out the way I envision would be very stressful for me. All the time spent on such a wonderful quilt deserves the best you can do. There's been good advice here. I agree with others that suggest FM in the darker areas or a more simple design that you are more sure of yourself. Maybe feathers in the dark areas instead of the light. However, "practicing" on a quilt brings on the rewards. It forces you to quilt better than you believe you can. And I have found it really looks pretty darn good when you step back a bit. Whatever you decide good luck to you. What a fun challenge you have ahead. Think how good you'll be after all that "practice". It will be beautiful I'm sure!

With a quilt this size, I would hesitate to attempt feathers if I was unsure. Do a design you are comfortable with on this one. Make a throw or twin size & practice the feathers on that.

That is a large quilt to tackle...we look forward to photos.
Jillmc, your log cabin turned out beautifully.

Log cabin quilting designs?
 

Here is as far as I got and have been procrastinating but tomorrow I will start on this quilt..Thanks everyone for your advice..
I am going to try and post a picture of the quilt so far..hope it works..