St-Sulpice is probably the best commune in the west of Lausanne (walking distance from EPFL) in terms of quality of life. Close to the lake shore, quiet neighborhood, and lowest income tax in the vicinity of Lausanne (probably in Vaud as well). The problem, of course, is that housing is very very expensive and difficult to find. Also, there is no Migros or Coop in this commune, just a grocery store in the center of the town. The closest metro stop is EPFL, which is about 20-30 minutes walk from the town center. So you really need a car to get around.
Ecublens is at the west of EPFL (the EPFL campus used to be included in Ecublens commune some time ago, although it is now included in Lausanne). Houses at the top of the hill have great view on the lake and they are correspondingly expensive. There are, however, smaller flats around Centre Commercial d'Ecublens, where you find large Coop, Migros, and Toys'R'Us stores among other things. Ecublens is a large commune in terms of surface area, and so the accessibility of metro depends on your exact location.
Chavannes-près-Renens is situated to the north of EPFL, and this district offers the highest chance of finding housing with decent price-to-quality ratio. M2 metro is easy to reach, and depending on the location, the Renens train station may also be close. The problem is that this commune is one of the poorer communes in the west Lausanne area, and suffers from high numbers of crimes and arson, mostly brought about by the adolescents who hang around at nights. The population is only about 50% of Ecublens, but the number of fires per year are almost equal. It seems that some buildings are especially inviting targets for the crimes, and so when visiting a flat, ask about burglary and arson. There are, however, still some nice neighborhoods if you look around.
Renens is to the north and east of Chavannes, and here you can also find cheaper flats, although many buildings would be very old. Renens is also a rather large commune, and so the quality of the neighborhood varies a lot depending on the location. What I've heard is that the old neighborhood (Renens-Village) is quite nice, while the neighborhood around the train station is not so great.
Prilly is sandwiched between Renens and Lausanne, and here the housing prices are also reasonable. When looking for housing, check that it's not right next to roads with a lot of traffic. There are two roads, namely Av de Florissant + Rte de Flumeaux, that look like normal small town roads but get jammed with traffic at the busy hours. There is also a regional train line (LEB) going through the commune. Prilly is situated on a hill side, and so biking is not really an option unless you enjoy torturing yourself.
One general comment about the west Lausanne area is that, if you have a car, you would tend to shop in Bussigny and Crissier, where you find huge Migros and Coop centers, Athleticum, MediaMarkt, and etc. Many shops are open until 19h30 on weekdays and until 18h on Saturdays.