Plus! offers a history feature but MSN also does. Can both be turned on at the same time without conflict? Which of the two is better?

yes, both can be activated. But what would be the point?
Both options are cool. Messenger Plus!' logs are plain and with no emotes, i like them better, they are easy to read. Messenger's logs have emotes and formatting... You decide

Often one of the first things I like to know when starting a chat is to review the history with that contact. If I want to acess it via Plus! I have to right click on the contact, go to Plus! in the menu and then History in the submenu whereas with the built in MSN history feature the last chat shows up in the chat window and previous history is accessible by pressing ine button...so in this respect I think MSN is more practical than Plus!....unless I'm missing something about Plus! regarding this...

nope, you aint missing anything
if you like to do that, then use Messenger's logs

Plus! logs are for people who dont check logs very often or like something plain and "light" better than a huge file with loads of emotes and unuseful stuff.

I agree that Plus! is better than MSN in that it's plain text, but MSN is more readily accesible...