I would not choose dips just to provide decompression. If you are really concerned with decompressing the spine, you can always just hang from a pull up bar or do a support hold in the top position of the dip with or without a little weight for traction.
I would only choose dips if they meet your needs for other reasons and you know you can tolerate them. Personally, I don't tolerate dips well and I think the standing press better develops the skills of rooting, wedging under the weight, and maintaining core stiffness.
If you want to do dips, Pavel has recommended doing them from a dead stop -- stand on a low box that places you in a bottom position you know you can tolerate well. Then you always have a reference point for a complete rep for that range of motion and you will know you aren't going too deep.
Another consideration in using dips for PTTP is figuring percentages for planning your cycles. Remember to include your body weight, not just the amount of added weight. So if you weigh 180 and want to start a cycle at 70%, your max needs to be at least BW + 80lbs.