I would definitely pay the extra money for the SM57. You example here shows the PG57 to have a very thin almost tinny sound while the SM57, as expected, has a deep robust full spectrum sound. It could be mic placement, but for me, $40 more is a small price to pay.
Just my opinion but you should only ever buy one cheap mic, to get you started off.
After that, buy something that you'll stick with. A SM57 will be used over and over again as it is a true pro level mic, if you can't get it to sound good, you're using it wrong. With a PG, you'll only end up wanting to upgrade in the future.
Of those two...I'd choose the PG57 for cleans and the SM57 for drive. However, in my experience the PG57 needs to be closer to the middle of the speaker than you have it there.
However...I wouldn't buy either of them for recording guitar. I'd much rather save an extra £30 or so and get a Sennheiser E906 In fact, I did a quick back-to-back of my Superlux PRA 628 (a £30 copy of the E906) against an SM57 I borrowed from our drummer, and I preferred the cheaper mic.
It's not always about money, it's about what you want from it. From my own experience, I haven't found a single mic which gets the sound I want in all situations.
There is a saying among sound engineers. “if you don’t what mic to use, use an SM57” they can mic anything and are as durable as hell. I’ve got 8 of the things and dude I’ve got to tell you I hardly use anything. Oddly SM57 really good for tin whistle
I completely agree with this, just want to add in the long run you don't save any money. SM57 are built like tanks, I have owned a shit ton and never had a single one fail (freelance live tech). they hold their value if you ever want to sell them on and they are simply the best all round instrument mic in the market.