I do not know any free transaction accelerator then ViaBTC, and I use it in past very successfully. But they are limited (in free version) in number of transaction per hour, and fact that they will not accept any transaction which has a fee lower then 10 000 satoshi.
As AdolfinWolf say, it is better to avoid any wallet that is not allow RBF(replace by fee), which is a very useful option if the transaction gets stuck. It is important to emphasize that this option should be enabled before sending the transaction.
What every user should do before sending a transaction is to check current status of network fees and mempool size. In that way you can adjust your fee according to your needs, for fast confirmation you will need to pay the highest fee, and if you can wait then you can adjust fee and reduce transaction costs.
Some users say that they exaggerate a bit, but I sometimes use this site because they show in simple way how much fee you should pay and predictions for confirmation in blocks / time. https://bitcoinfees.earn.com/
In short, if you want to avoid using transaction accelerators pay attention to what I mentioned
As AdolfinWolf say, it is better to avoid any wallet that is not allow RBF(replace by fee), which is a very useful option if the transaction gets stuck. It is important to emphasize that this option should be enabled before sending the transaction.
What every user should do before sending a transaction is to check current status of network fees and mempool size. In that way you can adjust your fee according to your needs, for fast confirmation you will need to pay the highest fee, and if you can wait then you can adjust fee and reduce transaction costs.
Some users say that they exaggerate a bit, but I sometimes use this site because they show in simple way how much fee you should pay and predictions for confirmation in blocks / time. https://bitcoinfees.earn.com/
In short, if you want to avoid using transaction accelerators pay attention to what I mentioned