Loch Lomond’s an hour and a half away from Edinburgh and not a particularly pleasant hour and a half at that, encompassing central belt motorway and some of the scummier weegie suburbs. I like North Queesnsferry – walk through shark tank is great, but having been in it with the sharks swimming around I am biased. Not the biggest, but a decent range of smaller tanks last time I was there, more than an hour’s entertainment probably nearer 2. Never been to the Loch Lomond one, but doubt if it can touch Nth Queesferry
Also, as you’re heading out to the bridge anyway, a trip to Inchcolm involves a boat trip under the bridges from Sth Queensferry which is pretty cool, but more money. Sth Queesferry is enough to spend an hour or so dotting about in anyway as long as the weather’s nice.
EDIT – St Andrew’s is further away, but just in case it was on your radar, don’t, it really is rubbish
EDIT again – can’t comment on Blair drummond, it’s been decades, but there is other stuff in the area to make that trip worthwhile, including Doune castle (Winterfell for Game of Thrones fans, also played several parts in Monty Python and the Holy Grail, audio tour guide is one of the Pythons) and the Ardgarty Red Kite feeder