Offers are better deal. Now, if you want to rush and be the superhero, then buy regular premium packs. You buy if does have money because as free player it is hard to save enough tokens even for the offers.
If you are lacking some epics sometimes is good to open but can do the same with the weekly's offers.
I buy offers time to time between months and be patient and accumulate them. No rush to be top just fun maxing parts farming.
Yesterday offer was a good offer for 3k tokens.
Some epic parts are in need for top mechs like that Hammer or the EMP with proper configurations in the picture provided.
If you do not know a lot, look the players sets at display and some videos and can give you some ideas of what you can do with what you have in your arsenal.
Play the game for fun does not rush and not thinking straight making mistakes eating parts. Try to manage properly parts.
Just in case, I do have premiums.