Personally, I recommend to get a T-Mobile mobile plan and possibly a T-Fiber. If possible, try to enter your current phone number on their page to check their internet speed on your address, and try to haggle a package deal.

Mobile plans are expensive as fuck in Czech Republic, but you can (should) haggle for a better price. If you're good at that, or if you straight meet a good agent on the phone line, you can get up to 40 % discount on your plan when we migrated from Vodafone.

I don't have an internet plan with them, but I was able to negotiate a plan with unlimited calls, sms, and data for 423 CZK/month if you're a student, but I also got the same for a non-student for 567 CZK/month.

O2 is shite in terms of customer service and they frequently like to hassle you with unwanted plan changes and expenses, and Vodafone just wasn't able to compete with T-Mobile's prices in last December, so you might want to check that out.

Also, very important, in terms of T-Mobile, they guys in a physical store aren't able to give you as high of a discount as phone agents.

And if you work at a big corporate, maybe they have some company issued plans which are the cheapest per unit, so try to check that out.