Should I force myself to learn to hold the deck in my left hand (will these be better in the long term?) or should I just go with what is more comfortable for me?
In many effects your right hand will play a lead role away from the cards such as providing instruction to your audience, misdirection etc. These actions will be much more natural with your dominant (right) hand.
If you're looking at getting some XCM moves down then the left hand often takes a passive roll ("just" holding the cards) with the right hand actively manipulating them. Training your left hand to take on this roll later on could be a challenge (not impossible though!).
Be patient as I'm sure you're already painfully aware hand skills can take a long time to develop - it's a frustration because you can't just read about something then do it - your mind adapts very quickly but your muscles, nerves, tendons etc take a lot longer to 'learn'.
I'm right handed but my left hand is now far more adept at certain manouvers than my right due to repeated practice.
That's my opinion also as a newcomer to card handling. I'm sure the pro's will put me straight.