"save it for later" is my favorite so far. It's cynical even by my standards, but the punchline is great. The other two don't do a whole lot for me, but they're not terrible.
When you let your panels get stretched like that, it really detracts from an otherwise good strip. Try to work on some techniques for reducing the amount of space your dialogue takes up. Eliminating unnecessary words helps. Using shorter words helps not only because it reduces letter count, but also because you're likely to be able to fit more of them on each line. Another option is to include a second character and split the text up into a dialogue, as long as it still makes sense. Alternately, some people keep the single character but put underscores_between_some_groups_of_words, because they form one long line which stretches the speech box sideways. I think you can use an instead of an underscore, but I've never actually tried it. Experiment and find out what works for you.