I have yet to check the train schedules and availability of ticket of KTM and ETS. But the choice is between a slow 3-hour (provided no delay) by KTM and a fast 2-hour by ETS. The fares are Rm15 and Rm26 for senior citizens respectively. But there is also the problem of no stops in KL (except the 6pm train) if I were to take ETS. So it is between taking a slower train but able to get off in Kepong or a faster train but having to take the Komuter from KL Sentral back to Kepong! Apart from finding out if the departure/arrival times suit me, the choice is quite clear that I would opt for KTM because I could get off between 15-30 minutes (my guess) before train reaches KL Sentral, rather than reaching KL Sentral earlier and having to take the Komuter back to Kepong (especially having read about occasional delays as complained by Komuter users).
Update: Don't take my word for the fares mentioned above though I remember having paid such fares before. Fares and schedules vary, depending on whether it is a weekday or weekend, or Class. I normally travel Superior (aka second class) and there is also Economy if by KTM, and I have just bought my ticket for ETS which is described as Premier! The fare for senior from BG to Kepong Sentral is Rm19. Btw, I have just found out that for Saturdays, trains leaving BG just after 10 am, 2pm and 4pm also stop at Kepong Sentral. Ticketing counters for both KTM and ETS are open from 8.00 am to 6.00 pm. and the telephone No: 05-3666616. It would be wise to call first to enquire whether ticket for specific time is available.