Can I take Claritin (loratadine) 24 hour with allegra 24 hour? I took the Claritin (loratadine) cause that's all I had but my husband bought allegra which I prefer.

Not if "D" formula. Often the number 24 refers to the "d" formulas. Claritin (loratadine) d24 and Allegra d 24 each contain 240 mg of pseudoephedrine, equivalent to 8 small red tablets of sudafed. You definitely wouldn't want to take 2 of the decongestant type of these medications in one day. On the other hand, taking one plain Claritin (loratadine) 10 mg and one plain Allegra 180 mg on the same day would be fine. Much more was used in tests.
No. Take one or other but not both during any given 24hr period of time. They're both from same family (antihistamines) so you don't want to duplicate medications & end up w/worse side effects, eg dry eyes, dry mouth, constipation & inability to urinate. As for which to take, that's a personal choice - as you noted, you get better results w/allegra but that's your metabolism. Keep plenty around!
Taking both together. Just wait 24 hours then switch over. Taking both together should not be a big problem but is unneccessary.