Personally, I'd go air hockey, but I like it better than pool. And I'd rather have a US/USSR Chexx table than both of those. 
Made in my hometown and the reason I can find MDO in stock at lumber yards here. I love bubble hockey.
As for the OP: How much use does the pool table get now? How often do you use it alone? If it gets a lot of solo play, I would say keep it.
The air hockey table will probably see a lot of action from guests at first as it is new, but then when that period wears off, will it still? Does the pool table still see heavy use, are your friends and family pool players outside of your house?
I have a pool table, it gets used at family parties. I've had it for 4 years now (it came with the house). Usage has declined with every year as the novelty has worn off. If your friends and family use it a lot maybe it is worth keeping.
In the end though...which do YOU like better? Do you have family (kids/spouse/etc) that will use one or the other regularly? Those are the real deciding questions to me.
If I had that choice I would swap it out as I like air hockey more than pool and since you don't need as much clearance around one I could fit one of those bubble hockey units also

Or...table football/soccer, I'd go with one of those...