I had this same problem since upgrading to 10.10.3 this week.
It seems to be 1 out of every 5 web pages is slow to load. Sometimes it is a few in a row. Sometimes 10 in a row are ok. Sometimes it is just about 1 in 5 or so. There is no rhyme or reason to it. The page will just start to load and the blue bar stops about 1/5 of the way across. If I put the cursor in the URL bar and hit enter, Safari snaps out of it and loads the page quickly. Sometimes even that fails, however (about 1 in 5 roughly). It is not isolated to one site, it is all of the sites I browse, rather evenly spread out.
I've never used Chrome before, but I just installed that. No issues at all. No other network apps seem to have problems, although the App Store seems intermittently slow. I'm not clear that's related at all.
Side by side, I can browse the same sites with Chrome and Safari, with Chrome always getting to the site quickly. Safari is always slower, but occasionally just freezing- and needing further action like described above to continue to make progress.
For now, I'm done with Safari. I have been telling everyone to use Safari because it is Apple's own browser, and that it MUST be more stable than a third party. After all, it is basically built into the OS. Not so much anymore.