Was that a typo? United and UA is the same airline, United Airlines. Did you mean to say US Airways for one of those two?

If you don't fly much and can't keep generating activities to all of your accounts, most will expire in 12- 24 months. Most of them are low enough that no savvy FTer will lose sleep over. So consider charity donation of your miles/points if you are going to lose them without expected activities anyway.

Which FFP to stick to depends on your goals. What is your use of miles? If only for domestic award tickets, I would say forget about Delta. You don't want to end up with miles you can't redeem after all the effort you put into.

If you can bump up your miles by getting credit card bonuses, you may turn some of your current miles to a redeemable level (25K for award tix or 12500 for one-way award on UA) and be done with it.

If you indeed had both UA and US miles, you should have credited all your miles into a major FFP since they are Star Alliance partners. When you fly, you should choose wisely to fly within the same alliance so you may credit all miles into one account.

For infrequent flyers, it's better to concentrate on one single program so you can achieve whatever goal you have in mind. Scattered miles in 5 different accounts get you no where.