To analyze competitors backlink portfolios, I use tools like Open Site Explorer, Yahoo Site Explorer, and Majestic SEO to pull my backlink lists for each competitor. Once I have my three lists, I scrub any duplicates and then begin looking at who is linking to this competitor and why. Once you have that, you can quickly see what each competitor is doing the best and apply it to your link building tactics.
Yeah now a days many seo competitor analyzer software. you can use them and save you time.. SEMrush seo tool one of them you can try it..
I have found chrome SEO very authentic in competitor analysis. It shows all results back links, Alexa Ranks and Page Ranks etc.
In addition to that, i have also check the back links from alexa.com. I check competitor's backlink by simply giving their site name into alexa search box, then i click inlinks for knowing the backlinks of them. Has any of you tried this?