1) Im using a 6mps mio home now n thinking to switch to a 100mbps or 200mps. Are they a big difference in speed??? Compared to my current 1 I think there is lol but which is more value for money?
One of the main differences between the 100Mbps and 200Mbps plan (apart from the local speed difference) is the international speed (15Mbps vs. 25Mbps respectively). If international speeds are of concern to you, which in some cases they are, then that might be the deciding factor.
Currently, I'm on the 200Mbps plan. Quite satisfied, although my surfing experience is being limited to WiFi. When surfing connected directly to my router (ONT -> 5012NV -> DIR-825), the speed really is addictive. Now, connecting to slower connections can become quite annoying.
2) the 2wire modem I'm using now is really problematic, I'm experiencing frequent dc... I'm so worried that switching to fibre don't really solve the issue ( if the problem lies with singtel ) . Do I need to replace the stock router they provide with a third party 1 to sustain a stable connection?
The 5012NV that SingTel provides is probably a marked improvement over the old mio box (2701HGV-E). In fact, the older, grey box (2700) was probably better than the white mio box. The new 5012NV is probably one of the residential gateways (RG) offered by telcos right now. It may not be on par with the fastest router available on the market, but it does a decent job.
You can take a look at other threads on how they've managed to overcome using the RG through the use of VLAN tagging, but if you use mio voice of mio TV, you need to get the right router (or router software) to do the work for you. Otherwise, if you have an existing router, it can piggyback on top of your RG, provided the IPs for both don't clash. Set it on DMZ (not DMZ Plus - that's notorious for capping speed) and you're good to go!
3) I'm surfing the net mostly on my iPhone... Anyone discover faster net browsing experience on iPhone using fibre?
You will probably see a moderate boost in surfing experience, although mobile devices are mostly limited to how fast they can process data. Download speeds might increase, but the bottleneck might transfer from the network to the processor rendering the web page.
On my Windows Phone, receiving and replying to notifications via WiFi is definitely faster than on 3G as are loading YouTube videos. Web pages, despite having a slightly snappier response after hitting the 'Return' key for a web site, still seems to be hampered by the processor processing the complexity of the site. Simple ones like CNA or YouTube mobile loads pretty quick, but media-rich ones like links to photo-sharing sites (YFrog, TwitPic, etc.) can often show a marginal improvement in response.