A filter is a lot lighter than a liter of water. The only problem is, you have to have water sources along your route for you to filter. That's not always the case on a day hike up a ridge in late summer. On the other hand, for a short hike you can probably get by just fine without drinking any water at all. The bottles and/or filter are for longer routes. There aren't many of those that don't have any water available.
Three or four liters should last you all day, even in the summer, unless your day hikes are of the thirty-mile type. Are you under-hydrated before you start? Consider downing a half-liter of Gatorade at the trailhead, and keep another one in a cooler in the car for when you finish the hike.
I've been happy with the Katadyn Hiker Pro for years, haven't looked at what else might be on the market. Easy to use, fits any bottle, low maintenance.
Besides the filter, I generally carry 1.5 liters of bottle capacity, and if I know my route I may hike with the bottles mostly empty between planned water stops. If I'm not sure I'll find water all day, I'll carry a little more, but I can't remember the last time I went over 3 liters.