I suppose in some ways it would be beneficial to swim in a larger pool but if time is a factor (which all ways is in training) I'd say stick to the closer pool. While you may have a larger pool to swim in you will have less time to actually swim. You could have a 100 yrd pool, but if you don't have the time to swim, you don't have the time to swim. Distance of the pool won't matter if you don't have the time.

20 yrds is small. I still would go with more time in the pool vs. the length of the pool.

I would probably go for the 50 yard pool, because twenty is just too small. Are you sure that it is 50 yards though, most large pools are 50 meters not yards. Just wanted to throw that out, because you don't want to think that you are swimming slower than you actually are. Hope this helps :-)

True, I guess it just depends on how much time you have and how imoprtant the size of the pool is to you. Personally a 20y pool would drive me crazy, but some would be able to manage just fine. To each his own!

Don't go for the 50yd pool. That drive can be a serious obstacle to training, and it doesn't really matter as much anyways. Just get in a couple of open water swims when you can, and you should be fine. Pool length differences are only really important to competitive swimmers.

I would focus on the small pool and try to get up to the bigger pool a couple times each month for a distance swim of some sort, paying a daily fee. 20 yards is indeed short. But like everyone says, you have to have time to train, and that commute to a pool for a workout could turnout to be a really easy way to bail on a workout. But try to get up to the bigger pool a few times. 50 meters or yards can feel like a long ways when you're used to 20.