If it were simply an option between nuclear or gas for that, nuclear would, generally, be the obvious choice. But it would be quite atypical to build a gas plant to provide base power. Typically they are being built to back up renewables.

Fair point that renewables may have a practical expansion limit, but for the time being are, by far, the cheapest option so a data centre is still going to prefer that source of power to the greatest extent possible, thereby leaving gas/nuclear only as reserve — of which nuclear has not proven to be cost effective at. Geothermal, hydro, etc. are hard to beat, but where you aren't sitting on the perfect environment, generally speaking, wind+solar+gas is about as good as it gets on a cost basis.