Who should I equip with 2030?

I would equip it on Tamamo or Jeanne. Lancelot would be better of with some CE with starting NP%

If you are relying on a single 2030 to generate enough star for the team, thats not very viable, though it will make star generating a lot more stable. Unless you have Saber Lancelot, having him is itself enough for a crit team as it simply generates enough star all by itself and to comsume it. Usually, it requires 2 copies of 2030 on 2 of your support to effectively form a crit team with decent stability, such example are like Merlin(2030), Waver(2030), DPS(Offensive CE). Without 2 copies of 2030, its stability is usually not high enough to make it replace other support CE such as prisma cosma.

It's a bit situationals without decently leveled Crit supp like Hans or Merlin there, consider raising unit like Hans for consistent crit gameplay. Hans equipped with 2030 is a beast of gameplay support, especially if you have his skill leveled more than 6/6/6 plus you're lucky enough to get Saberlot and 2030, that's some strong combination there. Alright, let's focus to use 2030 for your available unit here.

- Scathach - i would call this yes and no, because if you don't use Crit team when equipping her with 2030 then it's called no. If you have already made a Crit team then it's a yes. With 2030 and her decent hit count plus Crit team then it's already good.
- Musashi - 2030 is not a CE for her because she don't have passive Crit star drop up skill and her Crit star drop rate is tied with one of her most powerful skill. She's also a gorilla, you better equip 2030 to another competent Crit semi-support or another Crit unit.
- OG Chu Chulainn - he's NOT a Crit support nor a Crit star maker nor a Crit damage dealer, skip putting 2030 to him. His best place is on the backline and for emergency situations.
- Proto Chu Chulainn - he's like Lancelot but without Crit star gen kit, 3* Proto Chu is a beast of Crit damager and equipping a 2030 will increase his Crit consistency. Vs Archer then 2030 is one of the good CE for Chu.
- Tristan - he's a walking rain of Crit star, equip 2030 to him plus combined with his high hit count Quick deck then it's a good thing to do.
- Iskandar - meh, almost useless for him. His low hit count deck plus his Buster build making it worse, just equip him with a Golden Sumo or Limited Zero or Mona Lisa or any Buster CEs/Offensive CEs and something like that. Unless you're really2 desperate to make him into a Crit dealer then you're welcomed.
- Tamamo - a premiere support and one of the strongest servants of FGO alongside Skadi, Merlin and Waver. Her Bond CE, Prisma Cosmos and 2030 is one of the no-brainer CE option for her.
- King Hassan - see Iskandar description, equipping 2030 to a gorilla or survivalist is a big no. His single Quick card will rarely show on the battlefield, there are better unit like Jeanne and Hans or even Saberlot as 2030 holder. Let me remind you again, never put 2030 to a gorilla unless it's for experiments and having fun or you're really confident about your team then it's up to you.
- berserker Lancelot - a reminder, if you DON'T HAVE any good unit or any servants to cover him then don't even think to put him a CEs like 2030. If you have Vlad III Lancer equipped with any Crit star gen CEs like 2030 or etc on your friendlist then technically you're GG, with another crit supp and tank you can almost destroy everything. For example, Zerkerlot lvl 80 ( 2030 ) + friends Vlad III ( 2030 ) + Hans/Saberlot ( Crit star gen CEs ) + another tank like Mashu or Leonidas can be a freaking solid party for harder contents. One of berserker weakness is they need someone who can truly protect them from danger, Hercules or Chu Alter is an exception.
- Jeanne D'Arc a.k.a Jannu - Jannu is one of the best 2030 holder along with Merlin, Hans or even monster like Saberlot. Gameplay wise, Prisma Cosmos and NP gain CEs or 2030 is a no-brainer CE option for her.
For example, a team of Saberlot ( Onigashima + 15 % Crit damage Up plus gain 4 Crit stars per turn ) + friends Merlin/Hans 2030 + Jannu 2030 is totally a very consistent Crit team with freaking strong survivability. I would call this a juggernaut team, strong defense + strong offense it is just another GGWP.

Another reminder, for Crit teams servant like Hans or Caesar is one of the best unit to invest.
With Caesar you can even make any DPS or even Tank can hit freaking hard and with Hans, Crit will procc more often.