What metrics should be used to measure if a link is good or bad in SEO?

During link-building follow the below criteria and you could easily rank higher in SERP! 

1. Page Rank (not available as of now) / Domain Authority & Page Authority
2. Follow, Skip no follow websites. Even if PA & DA is high, no follow sites should be avoided.
3. External links below in order to get maximum link juice. (Still working)
4. Avoid banned sites (Porn, Online game, Casino)
5. Always go for content related webpages to link. (Google always check the landing page connection)

it's depand on your calculations and experience of your offpage work or work on your webmaster tool properly using 

Building links, then here are Metrics considered to confirm the link

1. Anchor text,(text Link) -exact match, brand etc
2. Position,(top fold, author),
3. relevancy & Niche (webpage and website level), prifer niche, generic if DA>
4. Do-follow or no-follow
5. contextual
6. DA> your website DA or DA >
7. Spam score (can verify using Moz Bar), >1
8. Traffic (geo Specific),
9. https:// or http://
10. Social media Shares
11. Permanent
12. Indexble or not indexed (buzzfeed)
13. link profile of source (to many external links is not decent) and let me know if any other metrics,

The link should redirect users to the correct destination as per described by the anchor text. The link should be relevant and answer what users are looking for. The link or content used should not be duplicate or spammy. The link should not lead to a 404 page. Then should look for other SEO metrics like the link is dofollow or nofollow, check its DA and TF, also check the spam score and overall seo score.

For me domain authority and incoming verified links are very important. 

You must 1st check its Page Rank and Domain Authority, its external links quantity and its niche. Also you can check its Alexa Rank

1. Total number of links
2. Number of unique domains
3. Linking domains vs total links
4. Anchor text usage and variance – branded, keyword rich, etc.
5. Fresh/incoming links
6. Page performance
7. Link quality*

Domain Authority by Moz and trust flow & citation flow by Majestic SEO can be used to measure the effectiveness of a link. Any link having domain authority less than20 is not that much useful...

You should use Ahref, MOZ, SEM Rush (Paid Tools) to measure the metrics of the link. The tools give you detailed information about Domain Authority, Page Authority, Page Rank etc... You can easily analyze the data. 

According to SEO Expert Metrics which you should Monitor to decide on Link Quality:1) Spam Score

2) Website Age

3) Relevant Nich

4) Domain Authority 

A link have several metrics to be classified as Good or Bad. Overall any link is good, but if its coming from a penalized site it can have negative affect.

A good link can be measured by Domain Authority (Higher the better) , Page Authority (higher the better) and Ahref Rank. First two metrics are provided by Moz, last one by Ahref. Both are paid tools.