Be aware that El Chalten is about a 3-4 hour drive from Calafate along ripio roads (crushed impacted gravel). If you're only there for 3-4 days, then a trip to Chalten is going to take up 2 x halves of those days.

Chalten is set up for individual hiking more than Calafate - you just walk out of town and you're in the park and practically in the hills at the base of FitzRoy. Calafate on the other hand is both larger and also a decent distance from nice hiking (unless you're staying at Los Notros).

Be careful at Calafate though - the local geography means that the weather can change very quickly - when we were there it went from sunny and still to 50 foot vis (in cloud), raining and very windy within an hour. Sorry, can't help with guides, etc for hiking around there - we just went off by ourselves.

My view would be that if you really want to go hiking (and you have some experience) then head up to Chalten - if you just want to have some nice walks, then stay around Calafate.

Either way, have a great trip.