From my very minimal knowledge, maybe Shas? Apparently they get some Arab votes so they seem like the religious party that would be least likely to cause trouble.
Why a Catholic would vote to get Israel on the theocracy path? I doubt than Jew religious parties are popular in the local Christian population.
Unless they're persecuting me, why wouldn't I want religious parties rather than secular ones in power even if they aren't my religion? Or are the religious parties in Israel hostile toward Christian minorities? Judaism doesn't seem big on converting everyone, so I doubt I'd need to worry about them trying to indoctrinate my family or something of that sort.
Of course this might be one of those times when writing this as an American has jaded my views to say something no one who actually lives in Israel would ever, ever say.
Shas wouldn't try to convert you, no, but you might have an awful lot of trouble getting married (civilly) or shopping on Saturday in a Shas-ruled Israel.
If he isn't Jewish then marrying won't be a problem, the second problem depends on whether he plans on living in a Jewish or Arab area.
Well, marriagewise there still could be a problem if he cannot find the right church, or if he wants to marry a Jew, for that matter
And living in an Arab area while voting for Shas could also be fun