Which is better and why?

It wont make a difference in PS3. In computers SDD is faster by a lot. But PS3 cant use SSDs advantages over HDD.

You want SSD it reduces weapon swap lag and reduces lag in general possibly improves planet loads but this is yet to be proven.

Im sure it doesn't. The lag is caused by the game itself not the console. So making the console faster/better wont affect the poorly made PS3 version of Deadlocked. But you can always try.

faster load time

It is faster, it does reduce lag and loads (mainly cutscenes but probably planet transitions) are faster on SSD

Skye IDK who you are even. Get in the Discord and join the hive mind so you can educate yourself before looking silly in this public forum LMAO https://discordapp.com/invite/jY7nS9F