T&M CLINS in Solicitation

I've seen various iterations of CLIN structures in T&M solicitations. Some Cost/Price Schedule CLINs provide the labor categories, and allow offerors to propose the labor rates and hours. I've seen Cost/Price Schedule CLINs provide the labor categories and the labor hours (for each category), and allow offerors to just propose the labor rates. Is there a "preferred" method?

Also, if the solicitation CLINs has the labor hours for each prospective labor category, could the offeror propose different labor hours?

There is no preferred method. Use the method appropriate for your acquisition.

I don't know if you can propose different hours. Instead of asking here you should ask the contracting officer who issued the solicitation. How should we know? Wait! Please tell me you're not writing a solicitation.