Bus transportation London to Bath

You should book your ticket in advance to guarantee a seat - on National you can also reserve a specific seat.

Both services have a toilet, but Flixbus in particular states it may not always be available.

As a matter of law no intercity bus in the UK can travel with standing passengers, but clearly every company wishes to have every seat full.

Flix Bus charter all their routes out to other operators, and the seat pitch can vary a lot depending on operator.

However you can, for an extra charge, book the seat next to you to be vacant.

National Express also charter out their routes, but with a consistent standard of vehicle (almost always in Nat Ex livery), and always with a toilet. So you know exactly what your seat will be like.
The 0900 is scheduled to be run by Edwards Coaches. They have no vehicles without toilets in their fleet. I've been on a lot of Edwards vehicles, the only thing is that more often than not the WiFi is not operative, but not a big problem on a 3 hour run.
It started that day on an 0350 from Bath to Victoria.
The 0700 is scheduled to be run by Chalfont Coaches- I've never been on one of their vehicles. While it should never ever be put on a NatEx route (especially on a first run of the day) they do apparently have some non toilet equipped vehicles (not in Nat Ex livery).

or the Paddington / Reading GWR railway train to Bath Spa has toilets in most coaches, disabled access in some. Smooth, no traffic, walk around if you like...

And only takes c75 minutes rather than 3 hours plus.

I agree with those suggesting the train- is there a reason you prefer the bus? The train also has much more frequent departures so you don't have to leave so early. As mentioned above, it's about half the time of the bus.

Thanks to everyone who has or who will respond to my question. The principle reason for only mentioning bus service at this time is because the place where I will be staying is about four blocks from the Victoria coach station which makes it is easy to take a bus to Bath. Also, depending on what time I will be willing to leave the fare can vary from $20 or less by bus to around $50 or more by train plus fare to Paddington station. Also, I wanted to hear complaints or praise that people who are familiar with these transportation options might have.

Take the train early and enjoy the city.

Booking reasonably in advance you should be able to get train tickets at around £25.

I wanted to hear complaints or praise that people who are familiar with these transportation options might have

I don't have any direct experience with the coach to Bath, but I have bags of experience of driving in and around the route. All I could say is Victoria to the Westway to M4, what could possibly go wrong?

I'd be on the train, even with an easy connection to Paddington - and I have shares in National |Express.

The train is better than the coach but the coach is fine. Some people prefer the coach because once you’re on and in your seat there is no stopping or people moving about. You can just listen to a book or podcast and relax until you get there. It does take longer though.

It’s really unlikely that you’ll find any cheap train fares on this route. It’s a popular route and significant discounts seem to be a thing of the past.

The bus isn't $20 each way, if you book ahead to the same time frames as the cheapest Advance rail tickets it can be as low as £5.20 each way (or less than $7).
If you turned up this morning a return fare on Nat Ex would be £40.80, on the train £75.90. On Flixbus today a walk up return is as low as £18 (£8 each way + the booking fee).

If you are over 60 you would buy a National Express coachcard for £17 and save 1/3 off those fares, same as the senior railcard. You seem to be doing this trip twice so on full fares would pay for itself.

Both Nat Express and Flixbus are perfectly good for a 3 hour trip- sure you can have little niggles, but equally so on a train- and the train (while unlikely) could be far more crowded than the bus- and the seats on GWR are far more uncomfortable than Nat Ex- but again for 75 minutes on the train, does that really matter?
The issue with the WiFi on Edwards coaches is much more of a problem when on the 9 hour trip from Penzance to Birmingham, but that is a 1st world problem.
Flixbus the inconsistent legroom is the biggest problem, slightly less good seats (but still far better than GWR) and in general (on longer runs) the lack of service station stops to save time.

Another vote for the train. See:>https://www.seat61.com/london-to-bath-by-train.htm

Helen - you might be right in general about cheaper train fares but I looked earlier at a random date in May and there were three mid morning trains with £25 fares available. The OP is clearly also in a position to book well ahead of his travel date. Of course that also applies to cheap bus fares as well. I’m biased - I really don’t enjoy long bus rides, especially on motorways.

Even if it cost a bit more, I'd take the train.

It's faster, more comfortable, plenty of toilets, more frequent.