Going for static fees is a "bad idea"™. The bitcoin network is a very dynamic system. Currently, fees are around 1-5 sats/byte... 6 months ago they were 1000 sats/byte. If you had static fees, there is a high probability that you will underpay during periods of high network activity and increasing fees (and end up with "stuck" transactions and long confirmation times)... and that you will overpay during periods of low network activity and decreasing fees (and pay way more for fees than you should).
In my opinion, a "good" wallet will provide "presets" that dynamically change with current network conditions so that casual users can simply choose a low/standard/high setting... but also provide a "custom" setting for more advanced users so they can specify exactly what the fee rate used will be.
There is a nice overview of how fee estimation within Bitcoin Core is handled (or was, prior to v0.15) here:
https://bitcointechtalk.com/an-introduction-to-bitcoin-core-fee-estimation-27920880ad0The article regarding what happened from v0.15 with regards to fee estimation is here:
https://bitcointechtalk.com/whats-new-in-bitcoin-core-v0-15-part-2-41b6d0493136