I only use Threebond 1207B on my race engines. It's the best there is for this job and it's what HRC use. High viscosity so easy to apply and copes with high temps. Its an RTV silicone based sealant.

Others I've used:

1104 - Synthetic rubber. Dangerous apparently and now production stopped. low viscosity, so messy stuff to use. I hate it, but many swear by it. Usually find more inside the cases than you actually put on in the first place. It's resistant to pretty much everything used in an engine. It's horrid. If you use this then you will spend more time cleaning it up than actually doing anything enjoyable.

1194 - Synthetic rubber. Replaces 1104. Haven't actually used this but put thought I'd mention it. I'm sure it's as nasty as 1104 but without the lead!

1211, 1212 - RTV Silicone based. 1212 has a higher viscosity than 1211, but other than that they're the same. Corrodes copper (1207 doesn't) so beware what you put it on.

Permatex Motoseal 1 - Possibly a sneaky copy of 1104/1194.

All these will work. But go for the 1207B if you can. You'll wince at the extra cost, but can be assured of top performance.