My advice would be roster spots until you’ve got a lot of headroom to roster characters… (I have between 160 and 170 spots and would likely buy more spots before I buy a heroic 10 pack)
Now for the unsolicited opinion: I’d strongly consider the 100HP daily deal and HfH store (depending on where your roster is at) before dumping on 10xheroics…
From previous comments, you are a fairly new player. So roster slots, roster slots and then more roster slots. By time you catch up with releases you’ll have 130 or so.
If you have all of the 3-5s already rostered (or empty slots for them to fill when you get them), your 2 farm up and running, a 1* for the DDQ and a MBW for TUs, and none of your 3s are close to 266, then I’d consider spending your HP on a Hero for Hire. Gets you the 4 you want and nets you a bunch of Elite tokens, which at the end of the day will net you similar results to a 10-pack considering you guarantee yourself a 4*.
If you don’t have all of the above then definitely go for slots. I’m at 133 slots myself, but I’m probably going to start buying more since 3 of my 3*s are over the 266 hump.
Roster slots… honestly, never buy the heroic 10-pack, the odds are awful, its quite expensive for what it is.
If you want to pull from heroics, use the daily deal (100hp, only once a day), you’ll save 1800 HP down the road. The “bonus” rate you get from a 10x is quite small.