With function calls, are system messages or description properties preferable to instruct AI?

    const response = await env.AI.run('@hf/nousresearch/hermes-2-pro-mistral-7b', {
        messages: [{
            role: "system",
            content: "Extract the user's favourite fruit and vegetable"
        }, {
            role: "user",
            content: 'I like pineapple, cars, carrots and Belgium.',
        }],
        tools: [{
            name: "say",
            parameters: {
                type: "object",
                properties: {
                    fruit: {type: "string"},
                    vegetable: {type: "string"},
                },
                required: ["fruit", "vegetable"],
            },
        }],
    });

    const response = await env.AI.run('@hf/nousresearch/hermes-2-pro-mistral-7b', {
        messages: [{
            role: "user",
            content: 'I like pineapple, cars, carrots and Belgium.',
        }],
        tools: [{
            name: "say",
            description: "Extract the user's favourite fruit and vegetable",
            parameters: {
                type: "object",
                properties: {
                    fruit: {type: "string", description: "The user's favourite fruit"},
                    vegetable: {type: "string", description: "The user's favourite vegetable"},
                },
                required: ["fruit", "vegetable"],
            },
        }],
    });