which is better text links or graphical links for seo?

Google pays close attention to link diversity, so it's better to have a single link from a wide variety of quality sites than many links from one site. Look for good link prospects from a diverse pool of sites.

1.WP Fastest Cache
2.Cache Enabler
3. W3 Total Cache
4.WP Super Minify
5.WP Smush.it
6.LazyLoad by WP Rocket
above all are the free plugin for increasing  page speed

I Personally would like to Recommend some of the best WordPress plugin for increasing speed:-

Google Pagespeed Insights

Google Pagespeed Insights is a Plugin that empowers you to make decisions that increase the performance of your website. Recommendations from Google Pagespeed are based upon current industry best practices for desktop and mobile web performance.
Speed Booster Plugin

Speed Booster Pack is a lightweight, frequently updated, easy to use and well supported plugin which allows you to improve your website's loading speed.
WP SpeedUP

WP SpeedUp is a great plugin to implement to install and forget about the page load speed issues. You can change settings from wp-admin or can leave it to default, you will feel significant difference in your website page load speed.