I do most of my on my iMac, while occasionally take my laptop outside for meetings and casual work/writing sessions in coffee shops around. The 12 MB does lag from time to time when handling medium to large Sketch files. Think 10 - 20 iPhone 6 screen size Artboards on a page, while the 13 rMBP handles most situations very well. However, I honestly think this is due to some poor file handling optimization from Sketch, rather than the lack of CPU power from the 12 MB. (Hope this could be improved overtime.)
I tend to not to do any serious work on laptops because the smaller screen sizes really limit my productivity. In my opinion, workstation is for work, laptop for portability.
Bottom line: Try to picture the scenarios when you'll use your laptop. If you see yourself spend hours working on it, then go with 13 rMBP. If you simply use your laptop as a companion sometimes, just to have a mac with you on-the-go like I do, then 12 MB will serve you just as well, with a smaller footprint and less impact on your spine/shoulder.
I have both the 13 rMBP, the 12 MB.
I do most of my on my iMac, while occasionally take my laptop outside for meetings and casual work/writing sessions in coffee shops around. The 12 MB does lag from time to time when handling medium to large Sketch files. Think 10 - 20 iPhone 6 screen size Artboards on a page, while the 13 rMBP handles most situations very well. However, I honestly think this is due to some poor file handling optimization from Sketch, rather than the lack of CPU power from the 12 MB. (Hope this could be improved overtime.)
I tend to not to do any serious work on laptops because the smaller screen sizes really limit my productivity. In my opinion, workstation is for work, laptop for portability.
Bottom line: Try to picture the scenarios when you'll use your laptop. If you see yourself spend hours working on it, then go with 13 rMBP. If you simply use your laptop as a companion sometimes, just to have a mac with you on-the-go like I do, then 12 MB will serve you just as well, with a smaller footprint and less impact on your spine/shoulder.