Team for Jack The Ripper?

Legitimately every offensive servant, since the crit stars she generates is just stupid good, meaning she ups the DPS and NP generation of the whole party (indirectly). For more specific cases though, anyone with the Self Modification skill to take advantage of the crit spam. Jeanne Alter is a great Jack friend since her own ability to crit is garbage.

Emiya with a leveled Hawkeye is another case, because he just sh*ts out huge damage with it active, but he can only make his own stars against weak mobs with UBW.

Jack works as an amazing star generator/secondary dps on any team really, so Jack/Waver/(any hard hitting unit) is a good team comp.

As for teams where Jack is the main attacker, against rider of female enemies, Jack/Waver/Scath is good.

Lancer Liz also is good support as between sadistic charisma and her Def debuff she really ups Jack output

As others have said, any good offensive servant works well with best daughter. On a quick brave chain, you very well can get over 50 crit stars, and her NP ranges from decent to insane damage depending on what you're fighting and can be spammable due to the charge gain she has.

Servants that specifically stand out would be any with a skill to increase crit star absorption and damage (Scathach, JAlter, Saberlot, etc.) Other choices would be either servants to keep her alive/more spammable (Waver, Tamamo, Mash) or servants that can also chain with her when she doesnt get a quick brave chain to keep the crits rolling regardless (Okita, MHX, Cursed Arm Hassan) or with star generation skills (Caster Bathory, Hans, etc.)

She's a great support, and that's been covered. If she's to be the star you can support her really well with Nero Bride, Caesar, Hans and Waver. The two sabers there are actually amazing supports for her and really shouldn't be overlooked. (I know Nero is super rare, but Caesar is easy enough to get and level.)